Post upgrade tasks refactor

Read the README for a full explanation of many of the changes / refactors I made.

Pipeline MR: https://repo1.dso.mil/platform-one/big-bang/pipeline-templates/pipeline-templates/-/merge_requests/186

Essentially:

Move functions.sh into scripts and add this folder to path before renovate is run. See: renvate.yaml

The scripts folder is used as commands in postUpgradeTasks. See: example.renovate.json for an example.

Renovate config has been consolidated to config.js from primarily being in ENV variables.

A default.json has been created for renovate config inheritance/extending. See: example.renovate.json for an example.