meta(make): Add help messages to Makefile

[olksdr]

Adding useful documentation or help messages to the Makefile will help
contributors to quickly check all the available targets and what exactly
they do without opening the file itself.

Now one can just run make help to get the beautiful help message, like :

❯ make help
Usage: make <target>
Targets:
  all                   run all checks and tests
  check                 run the lints and check the code style for rust and python code
  clean                 remove python virtual environment and delete cached rust files together with .target folder
  build                 build relay with all features enabled with debug info
  release               build production release of the relay with

...

#skip-changelog

[olksdr]

closing in favour of #1419