[KAG-2033] Deprecate CentOS 7 Packages

[curiositycasualty]

Summary

This PR sunsets references to, and build configuration for, CentOS 7 rpm packages.

Checklist

• [na] The Pull Request has tests
• [na] There's an entry in CHANGELOG-EE.md
• [na] There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE
• [na] The Pull Request has backports to all the versions it needs to cover

Full changelog

• [Deprecate CentOS 7]

Issue reference

Fix #KAG-2033

[curiositycasualty]

Do I need backports for this? This change is meant to affect all 3.x versions of both editions of the gateway.

[fffonion]

@curiositycasualty let's do backport for 3.4.x only

[team-gateway-bot]

The backport to release/3.4.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/3.4.x release/3.4.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.4.x
# Create a new branch
git switch --create backport-11359-to-release/3.4.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 62b64887826555874f15ad6203182dd665c5ac1a
# Push it to GitHub
git push --set-upstream origin backport-11359-to-release/3.4.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.4.x

Then, create a pull request where the base branch is release/3.4.x and the compare/head branch is backport-11359-to-release/3.4.x.