Support indexing pressure on NodeStats

[stevejgordon]

Indexing pressure stats were added in 7.9.0
elastic/elasticsearch#59467

They were updated to include memory limit stats in 7.10.0
elastic/elasticsearch#60342

Contributes to #5096

[Mpdreamz]

While I think inner classes are the best choice stylistically once we shift from hand rolling these to generating these it will be hard to know when inner classes are preferred.

I hate saying it but smurf types are better here

[stevejgordon]

That's a new term for me 😄

[stevejgordon]

I've moved out to non-nested classes @Mpdreamz. If this change is what you expected, hopefully we're good to merge.

[Mpdreamz]

LGTM, I left one comment about value type properties might needing to be nullable depending on wheter they are always present or not.

[github-actions]

The backport to master 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-master master
# Navigate to the new working tree
cd .worktrees/backport-master
# Create a new branch
git switch --create backport-5148-to-master
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick ---mainline 1 de02c9de8d218a3de8a05d1214c7c8b81fe51697
# Push it to GitHub
git push --set-upstream origin backport-5148-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-5148-to-master.