Additional changes related to porting from AWS, whether past or present.

Migrated SW_INSTALLS.md about user persistent kernel creation scripts which are built into the image but really only apply to the hub.
Removed instance of CLEAR_PKG_CACHES from infrequent-env. Ported new ruff source code scanning.
Added ruff to requirements.txt.
Ported new branch-changes-obj script.
Dropped git-remote-codecommit unneeded for GitHub from requirements.txt

spacetelescope / science-platform-images