fix(balancer) use local target cache

[locao]

Summary

The target's global cache was caching more data than it should: it kept data retrieved from the database and DNS name resolution, which has its own cache.

As a result, when config reloads were done, some processes were skipped (such as setting the upstream as healthy) because the load-balancer never identified the data as new if it was the same as cached (highly probable with DNS name resolution).

This change makes the target cache local to the worker.

Checklist

• The Pull Request has tests
• There's an entry in the CHANGELOG
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Full changelog

• Make the target cache local to the worker.
• This PR has no tests. This is a race condition, almost impossible to automate.

Issue reference

FTI-3172
Fix #8517
Fix #10020

[team-gateway-bot]

The backport to release/2.8.x 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/2.8.x release/2.8.x
# Navigate to the new working tree
cd .worktrees/backport-release/2.8.x
# Create a new branch
git switch --create backport-10384-to-release/2.8.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 4f29d72d00b3278a2c12fb67a073c3c985f5b434
# Push it to GitHub
git push --set-upstream origin backport-10384-to-release/2.8.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/2.8.x

Then, create a pull request where the base branch is release/2.8.x and the compare/head branch is backport-10384-to-release/2.8.x.