tests(helpers): separate cmd&pid functions

[chronolaw]

Summary

KAG-5244

Move echo server related functions since they are using cmd.stop_kong()

Checklist

• 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
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #[issue number]

[StarlightIbuki]

I suppose we will also update the user of those utilities to directly import from separated files, to avoid unnecessary dependencies?

[chronolaw]

I suppose we will also update the user of those utilities to directly import from separated files, to avoid unnecessary dependencies?

It may cause incompatible issues, currently we will not change the interface of helpers.

[team-gateway-bot]

Cherry-pick failed for master, 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 master
git worktree add -d .worktree/cherry-pick-13648-to-master-to-upstream upstream/master
cd .worktree/cherry-pick-13648-to-master-to-upstream
git checkout -b cherry-pick-13648-to-master-to-upstream
ancref=$(git merge-base c498f41dc03f7a04aaf3df24c59e01ff5e39c339 3bd7ce5b076eee1f3658187864998c3c53f1dafc)
git cherry-pick -x $ancref..3bd7ce5b076eee1f3658187864998c3c53f1dafc