Closes#167075
## Summary
Adds a public asset client available in the `setup` lifecycle hook for
plugins that depend on this one. `getHosts` is the only method available
on this client for now.
TODO, before merge:
- [x] Add docs for the server client
- [x] Add docs for the public client
- [x] Remove REST docs from plugin docs, not needed
- [x] Add unit tests for public client
### Testing this PR
One way of testing this new client is to apply the attached
test-assets.patch file locally, adjust the date range in the getHosts
query that is added in the infra plugin, and then start Kibana and
navigate to the infra app. You should see print out in the browser
console.
[test-assets.patch](12718693/test-assets.patch)
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Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>
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