#145: bug_and_feature/pre_gen_project_hook - adding hook script to validate infrastructure_slug

[gregoryfoster]

Link to Relevant Issue

https://github.com/CouncilDataProject/cookiecutter-cdp-deployment/issues/145

Description of Changes

• Adds hooks/pre_gen_project.py
• Validates infrastructure_slug is <= 30 characters, the limit for Google Cloud Project names

Test by running the cookiecutter template and entering a very long infrastructure_slug; you won't see feedback until after entering all input variables, when this hook script is executed.

[evamaxfield]

Thanks!!