Adding geo_grid query

[l-trotta]

Server code: https://github.com/elastic/elasticsearch/blob/main/x-pack/plugin/spatial/src/main/java/org/elasticsearch/xpack/spatial/index/query/GeoGridQueryBuilder.java

[github-actions]

The backport to 8.16 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-8.16 8.16
# Navigate to the new working tree
cd .worktrees/backport-8.16
# Create a new branch
git switch --create backport-3860-to-8.16
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 5b9a58f8c4ed77a65cd85372e383774745caed52
# Push it to GitHub
git push --set-upstream origin backport-3860-to-8.16
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.16

Then, create a pull request where the base branch is 8.16 and the compare/head branch is backport-3860-to-8.16.