Fix EnableSourceMaps and add EnableMinify parameter

[tmclaugh]

Discovered in ServerlessOpsIO/serverlessops-catalog-api#8

Because we don't pass --parameter-overrides to sam build when running yarn run sam:build anything we have set in cfn-parameters.json is ignored. Possible solutions:

• Document in template.yaml the need to change values there. This unfortunately leaves the issue in place.
• Incorporate cfn-parameters.json handling local to project and pass parameter overrides to build command.
• Replace yarn run sam:build usage in pipeline with a GHA action.

While here, add EnableMinify parameter which will work similarly.