[Resolve #746] add before_launch and after_launch hooks

[cornerman]

Add before_launch and after_launch hooks to do something whenever the stack is run.

PR Checklist

• Wrote a good commit message & description [see guide below].
• Commit message starts with [Resolve #issue-number].
• Added/Updated unit tests.
• Added/Updated integration tests (if applicable).
• All unit tests (make test) are passing.
• Used the same coding conventions as the rest of the project.
• The new code passes flake8 (make lint) checks.
• The PR relates to only one subject with a clear title.
  and description in grammatically correct, complete sentences.

Approver/Reviewer Checklist

• Before merge squash related commits.

Other Information

Guide to writing a good commit

[zaro0508]

I've tested with my project and this seems to be working as I would expect. @ngfgrant can we merge?

[ngfgrant]

yep lets resolve docs/_source/docs/hooks.rst and ill merge it in

[cornerman]

yep lets resolve docs/_source/docs/hooks.rst and ill merge it in

@ngfgrant resolved :)