Sustainable Kibana Architecture: Move modules owned by @elastic/security-generative-ai (#202848)

## Summary

This PR aims at relocating some of the Kibana modules (plugins and
packages) into a new folder structure, according to the _Sustainable
Kibana Architecture_ initiative.

> [!IMPORTANT]
> * We kindly ask you to:
> * Manually fix the errors in the error section below (if there are
any).
> * Search for the `packages[\/\\]` and `plugins[\/\\]` patterns in the
source code (Babel and Eslint config files), and update them
appropriately.
> * Manually review
`.buildkite/scripts/pipelines/pull_request/pipeline.ts` to ensure that
any CI pipeline customizations continue to be correctly applied after
the changed path names
> * Review all of the updated files, specially the `.ts` and `.js` files
listed in the sections below, as some of them contain relative paths
that have been updated.
> * Think of potential impact of the move, including tooling and
configuration files that can be pointing to the relocated modules. E.g.:
>     * customised eslint rules
>     * docs pointing to source code

> [!NOTE]
> * This PR has been auto-generated.
> * Any manual contributions will be lost if the 'relocate' script is
re-run.
> * Try to obtain the missing reviews / approvals before applying manual
fixes, and/or keep your changes in a .patch / git stash.
> * Please use
[#sustainable_kibana_architecture](https://elastic.slack.com/archives/C07TCKTA22E)
Slack channel for feedback.

#### 1 plugin(s) are going to be relocated:

| Id | Target folder |
| -- | ------------- |
| `@kbn/elastic-assistant-plugin` |
`x-pack/solutions/security/plugins/elastic_assistant` |




#### 3 packages(s) are going to be relocated:

| Id | Target folder |
| -- | ------------- |
| `@kbn/elastic-assistant` |
`x-pack/platform/packages/shared/kbn-elastic-assistant` |
| `@kbn/elastic-assistant-common` |
`x-pack/platform/packages/shared/kbn-elastic-assistant-common` |
| `@kbn/langchain` | `x-pack/platform/packages/shared/kbn-langchain` |


<details >
<summary>Updated references</summary>

```
./.buildkite/scripts/steps/code_generation/elastic_assistant_codegen.sh
./.buildkite/scripts/steps/openapi_bundling/security_solution_openapi_bundling.sh
./.eslintrc.js
./.github/codeql/codeql-config.yml
./docs/developer/plugin-list.asciidoc
./oas_docs/scripts/merge_ess_oas.js
./oas_docs/scripts/merge_serverless_oas.js
./package.json
./packages/kbn-repo-packages/package-map.json
./packages/kbn-ts-projects/config-paths.json
./tsconfig.base.json
./tsconfig.base.type_check.json
./tsconfig.refs.json
./x-pack/.i18nrc.json
./x-pack/packages/kbn-elastic-assistant-common/README.md
./x-pack/platform/packages/shared/kbn-elastic-assistant-common/README.md
./x-pack/platform/packages/shared/kbn-elastic-assistant-common/env/README.md
./x-pack/platform/packages/shared/kbn-elastic-assistant-common/impl/capabilities/README.md
./x-pack/platform/packages/shared/kbn-elastic-assistant-common/jest.config.js
./x-pack/platform/packages/shared/kbn-elastic-assistant/README.md
./x-pack/platform/packages/shared/kbn-elastic-assistant/jest.config.js
./x-pack/platform/packages/shared/kbn-langchain/jest.config.js
./x-pack/plugins/elastic_assistant/README.md
./x-pack/plugins/security_solution/docs/openapi/README.md
./x-pack/solutions/security/plugins/elastic_assistant/README.md
./x-pack/solutions/security/plugins/elastic_assistant/jest.config.js
./x-pack/solutions/security/plugins/elastic_assistant/scripts/create_conversations_script.ts
./x-pack/solutions/security/plugins/elastic_assistant/server/__mocks__/docs_from_directory_loader.ts
./x-pack/solutions/security/plugins/elastic_assistant/server/knowledge_base/security_labs/embedding_security_in_llm_workflows.md
./x-pack/solutions/security/plugins/elastic_assistant/server/lib/attack_discovery/graphs/default_attack_discovery_graph/index.ts
./yarn.lock
```

</details><details >
<summary>Updated relative paths</summary>

```
x-pack/platform/packages/shared/kbn-elastic-assistant-common/jest.config.js:21
x-pack/platform/packages/shared/kbn-elastic-assistant-common/scripts/openapi/bundle.js:8
x-pack/platform/packages/shared/kbn-elastic-assistant-common/scripts/openapi/generate.js:8
x-pack/platform/packages/shared/kbn-elastic-assistant-common/tsconfig.json:2
x-pack/platform/packages/shared/kbn-elastic-assistant/jest.config.js:21
x-pack/platform/packages/shared/kbn-elastic-assistant/tsconfig.json:15
x-pack/platform/packages/shared/kbn-elastic-assistant/tsconfig.json:2
x-pack/platform/packages/shared/kbn-langchain/jest.config.js:20
x-pack/platform/packages/shared/kbn-langchain/tsconfig.json:2
x-pack/solutions/security/plugins/elastic_assistant/jest.config.js:14
x-pack/solutions/security/plugins/elastic_assistant/scripts/create_conversations.js:8
x-pack/solutions/security/plugins/elastic_assistant/scripts/draw_graph.js:8
x-pack/solutions/security/plugins/elastic_assistant/scripts/model_evaluator.js:8
x-pack/solutions/security/plugins/elastic_assistant/tsconfig.json:13
x-pack/solutions/security/plugins/elastic_assistant/tsconfig.json:2
```

</details>

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

docs/developer/plugin-list.asciidoc

@@ -557,7 +557,7 @@ Plugin server-side only. Plugin has three main functions:
 |This plugin implements (server) APIs used to render the content of the Data Quality dashboard.
 
 
-|{kib-repo}blob/{branch}/x-pack/plugins/elastic_assistant/README.md[elasticAssistant]
+|{kib-repo}blob/{branch}/x-pack/solutions/security/plugins/elastic_assistant/README.md[elasticAssistant]
 |This plugin implements (only) server APIs for the Elastic AI Assistant.