makefile: breakout some common functionality into includable file

[doshitan]

Changes

Example for consolidating some shared functionality between a bunch of template makefiles.

Could be built on with a file for common docker stuff, desired common targets (e.g., lint, test) etc. to further streamline application makefiles.

TODO:

• Not sure how realistically different projects would need to do something radically different for the help target, so could have that defined by default? Or maybe include a standard help alias for help-standard in a different lib file?
• Might want to breakout into a separate repo for other platform templates that don't use template-infra?

Testing

Run some make commands.