Fix: Replace missing systemd Unit File (2.8)

[curiositycasualty]

Summary

This PR fixes an issue where the systemd unit file, kong.service, had gone missing from packages produced from the 2.8 branch(es).

Checklist

• [na] The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• [na] There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #KAG-5648

[curiositycasualty]

Issue first raised (to me) in #13464

The EE cherry pick will need the explain_manifest changes expanded for non-CE platforms of that repo.

[team-gateway-bot]

Cherry-pick failed for release/2.8.x: couldn't find remote ref release/2.8.x.
Please ensure that this Github repo has a branch named release/2.8.x.

[team-gateway-bot]

Cherry-pick failed for release/2.8.x, because it was unable to create a new branch.

Please cherry-pick the changes locally.

git remote add upstream https://github.com/kong/kong-ee
git fetch upstream release/2.8.x
git worktree add -d .worktree/cherry-pick-13778-to-release/2.8.x-to-upstream upstream/release/2.8.x
cd .worktree/cherry-pick-13778-to-release/2.8.x-to-upstream
git checkout -b cherry-pick-13778-to-release/2.8.x-to-upstream
ancref=$(git merge-base 930ca76e3c296fa6816fc9f37e0384b57578ffba e09e3d5cbe9a6e9660060caacb507b71e2298c54)
git cherry-pick -x $ancref..e09e3d5cbe9a6e9660060caacb507b71e2298c54

[team-gateway-bot]

Cherry-pick failed for release/2.8.x, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally.

git remote add upstream https://github.com/kong/kong-ee
git fetch upstream release/2.8.x
git worktree add -d .worktree/cherry-pick-13778-to-release/2.8.x-to-upstream upstream/release/2.8.x
cd .worktree/cherry-pick-13778-to-release/2.8.x-to-upstream
git checkout -b cherry-pick-13778-to-release/2.8.x-to-upstream
ancref=$(git merge-base 930ca76e3c296fa6816fc9f37e0384b57578ffba e09e3d5cbe9a6e9660060caacb507b71e2298c54)
git cherry-pick -x $ancref..e09e3d5cbe9a6e9660060caacb507b71e2298c54

[team-gateway-bot]

'git push --set-upstream upstream cherry-pick-13778-to-release/2.8.x-to-upstream' failed with exit code 1

[curiositycasualty]

Upon further inspection, the systemd unit is named kong-enterprise-edition.service in EE and exists in all the images I tested already, nullifying the need for the EE cherry-pick:

for t in {kong,kong/kong-gateway}:{2.8,3.{8..4}}-ubuntu; do printf '%-50s%s\n' "${t}~" '~' | tr ' ~' '- '; podman run --user=root --platform linux/amd64 -e KONG_DATABASE=off --rm -it $t bash -c 'find / -name "kong*.service"'; done
kong:2.8-ubuntu ----------------------------------
kong:3.8-ubuntu ----------------------------------
/usr/lib/systemd/system/kong.service
kong:3.7-ubuntu ----------------------------------
/usr/lib/systemd/system/kong.service
kong:3.6-ubuntu ----------------------------------
/usr/lib/systemd/system/kong.service
kong:3.5-ubuntu ----------------------------------
/usr/lib/systemd/system/kong.service
kong:3.4-ubuntu ----------------------------------
/usr/lib/systemd/system/kong.service
kong/kong-gateway:2.8-ubuntu ---------------------
/usr/lib/systemd/system/kong-enterprise-edition.service
kong/kong-gateway:3.8-ubuntu ---------------------
/usr/lib/systemd/system/kong-enterprise-edition.service
kong/kong-gateway:3.7-ubuntu ---------------------
/usr/lib/systemd/system/kong-enterprise-edition.service
kong/kong-gateway:3.6-ubuntu ---------------------
/usr/lib/systemd/system/kong-enterprise-edition.service
kong/kong-gateway:3.5-ubuntu ---------------------
/usr/lib/systemd/system/kong-enterprise-edition.service
kong/kong-gateway:3.4-ubuntu ---------------------
/usr/lib/systemd/system/kong-enterprise-edition.service