Implement ml.estimate_model_memory.json

[codebrain]

Implements: https://www.elastic.co/guide/en/elasticsearch/reference/7.x/ml-estimate-model-memory.html

[russcam]

Left some comments

[github-actions]

The backport to master failed:

The process '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-master master
# Navigate to the new working tree
cd .worktrees/backport-master
# Create a new branch
git switch --create backport-4530-to-master
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 035e4bca5fab292ee3135c8c92c54289a3019f9d
# Push it to GitHub
git push --set-upstream origin backport-4530-to-master
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-master

Then, create a pull request where the base branch is master and the compare/head branch is backport-4530-to-master.

[codebrain]

Manually backported to master