While the internal structure of the docs is already split into many (over 1000) sub-pages, the final display for the `Functions and Operators` page is a single giant page, making navigation harder. This PR splits it into separate pages, one for each group of similar functions and one for the operators. Twelve new pages.
This PR also bundles a few other related changes. In total what is done is:
* Split functions/operators into 12 pages, one for each group, maintaining the existing split of each function/operator into a snippet with dynamically generated examples
* Split esql-commands.md into source-commands.md and processing-commands.md, each of which is split into individual snippets, one for each command
* Each command snippet has it's examples split out into separate files, if they were examples that were dynamically generated in the older asciidoc system
* The examples files are overwritten by the ES|QL unit tests, using a similar mechanism to the examples written for functions and operators)
* Some additional refinements to the Kibana definition and markdown files (nicer operator headings, and display text)
This primarily splits the old preview:true warning from the newer applies_to approach. Since all of our current applies_to examples are actually just behaviour modifications of current functions, we do not use the official docs {applies_to} syntax. However there is code to make use of that in the case where we have an entirely new function which will appear in a new version.
Co-authored-by: Alexander Spies <alexander.spies@elastic.co>
This PR was originally focused on improving support for Kibana docs, in particular the missing operator docs, but it has expanded to cover a bunch of related things:
* Primarily the main work was to improve operators support. ESQL generated docs cover all functions and most operators for which their is a clear operator class and test class. However, some are built-in behaviour and need additional support. This PR adds more generated content for those operators.
* Various specific operators requested by Kibana: Cast & null-predicates, and in particular the addition of examples
* Two functions without examples: mv_append and to_date_nanos
* Many small visual document cleanups (spelling, grammar, capitalization, etc.)
* Initial support for `applies_to` for multi-version differentiation.
This last point requires more work, as it is not yet agreed on just how we want this to look. We'll probably need to do refinements in followup PR. Consider the version in this PR as a first step into how this could look.
In a few previous PR's we restructured the ES|QL docs to make it possible to generate them dynamically.
This PR just moves a few files around to make the query languages docs easier to work with, and a little more organized like the ES|QL docs.
A bit part of this was setting up redirects to the new locations, so other repo's could correctly link to the elasticsearch docs.
Building on the work started in https://github.com/elastic/elasticsearch/pull/123904, we now want to auto-generate most of the small subfiles from the ES|QL functions unit tests.
This work also investigates any remaining discrepancies between the original asciidoc version and the new markdown, and tries to minimize differences so the docs do not look too different.
The kibana json and markdown files are moved to a new location, and the operator docs are a little more generated than before (although still largely manual).
