Add private capabilities API

[pquentin]

For rest-api-spec generation purposes. Resources:

• https://github.com/elastic/elasticsearch/blob/main/rest-api-spec/src/main/resources/rest-api-spec/api/capabilities.json
• Example recording: https://github.com/elastic/clients-flight-recordings/blob/7c05d92d8e8646e3c62c366989041f477eed0531/elasticsearch/capabilities/cd45462a690d8bab645e9e14665f7e31.json
• Request: https://github.com/elastic/elasticsearch/blob/e6c5dcc087f13a3cfe738ab1531e4ab7ed39a0de/server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestNodesCapabilitiesAction.java#L56-L75
• Response: https://github.com/elastic/elasticsearch/blob/main/server/src/main/java/org/elasticsearch/action/admin/cluster/node/capabilities/NodesCapabilitiesResponse.java

[github-actions]

Following you can find the validation changes against the target branch for the API.

API	Status	Request	Response
capabilities	➕ 🟢	2/2	2/2

You can validate this API yourself by using the make validate target.

[l-trotta]

I'm not 100% sure, but I'm wondering if this also supports a failures field as a list of exceptions. https://github.com/elastic/elasticsearch/blob/4c1c51e87001f4df27667ad23e40729071646faa/server/src/main/java/org/elasticsearch/action/support/nodes/BaseNodesResponse.java#L98

[pquentin]

Maybe? I haven't been able to find the toXContent() code. I've added failures. Not too worried, since it's a private API.

[MattDevy]

Prettier needs running for formatting, otherwise LGTM!

[github-actions]

The backport to 8.19 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-8.19 8.19
# Navigate to the new working tree
cd .worktrees/backport-8.19
# Create a new branch
git switch --create backport-5741-to-8.19
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a245ec050696cdb7ff00a3b887e7ec31afc57183
# Push it to GitHub
git push --set-upstream origin backport-5741-to-8.19
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.19

Then, create a pull request where the base branch is 8.19 and the compare/head branch is backport-5741-to-8.19.

[pquentin]

💚 All backports created successfully

Status	Branch	Result
✅	8.19

Questions ?

Please refer to the Backport tool documentation