fix(metrics): drop stale datapoints

[swiatekm]

Prometheus and prometheus receiver emit staleness markers in the form of samples with a NaN value whenever a target disappears. These markers aren't that useful when a target is moved between collector Pods, and Sumo currently doesn't handle them correctly.

Drop them in the collector instead.

Checklist

• Changelog updated or skip changelog label added
• Template tests added for new features

[sumo-backporter]

The backport to release-v3 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-release-v3 release-v3
# Navigate to the new working tree
cd .worktrees/backport-release-v3
# Create a new branch
git switch --create backport-3318-to-release-v3
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 70af83f69e2b856d4173fdfd3e11739de47b8a43
# Push it to GitHub
git push --set-upstream origin backport-3318-to-release-v3
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release-v3

Then, create a pull request where the base branch is release-v3 and the compare/head branch is backport-3318-to-release-v3.