Add stable/2402 branch and remove stable/2306 branch to docker executor image scripts

Add stable/2402 branch and remove stable/2306 branch to docker executor image scripts

- Refactor csit_pip_cache function to use csit bash
  functions that activate the python virtualenv in
  production jobs.
- Remove stable/2306 branch due to pip issue
  https://github.com/pypa/pip/issues/11527
  causing extraneous downloading of pip wheels in
  CSIT jobs.
- Remove installation of packages for old CSIT docs
  generation.

Change-Id: Ib63aa654a35ad01fbfb5b7f593d3f8ffa6499b07
Signed-off-by: Dave Wallace <dwallacelf@gmail.com>