Update inference API descriptions to include new Mistral task types

[Jan-Kazlouski-elastic]

Following up on #4519 PR. Adding new task types for Mistral AI Inference Integration: "completion" and "chat_completion".

[github-actions]

Following you can find the validation results for the API you have changed.

API	Status	Request	Response
inference.put	⚪	Missing test	Missing test

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

[github-actions]

Following you can find the validation results for the API you have changed.

API	Status	Request	Response
inference.put	⚪	Missing test	Missing test

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

[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-4529-to-8.19
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 18b631e0bb4c66c36ed37557e688974396b102e6
# Push it to GitHub
git push --set-upstream origin backport-4529-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-4529-to-8.19.