Add support for make help

[saschagrunert]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Add a nice make help output like this:

Usage:
  make <target>
  help                       Display this help.

Build targets:
  default                    Build in debug mode.
  release                    Build in release mode.
  release-static             Build the static release binary.

Test targets:
  unit                       Run the unit tests.
  integration                Run the integration tests using the release binary.
  integration-static         Run the integration tests using the static release binary.

Verify targets:
  lint                       Lint Rust and Go sources.
  lint-rust                  Lint the Rust sources.
  lint-go                    Lint the Go sources.
  verify-dependencies        Verify the local dependencies.
  verify-prettier            Run prettier on the project.

Utility targets:
  prettier                   Prettify supported files.
  clean                      Cleanup the project files.
  update-proto               Update the Cap'n Proto protocol.
  create-release-packages    Create the release tarballs.
  install                    Install the binary.
  nixpkgs                    Update the NIX package dependencies.

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

None

Does this PR introduce a user-facing change?

None

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: saschagrunert

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [saschagrunert]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 47.76%. Comparing base (4e0f474) to head (37887ed).
Report is 716 commits behind head on main.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2409       +/-   ##
===========================================
+ Coverage   37.53%   47.76%   +10.22%     
===========================================
  Files          15      121      +106     
  Lines        1268     4007     +2739     
  Branches      414      830      +416     
===========================================
+ Hits          476     1914     +1438     
- Misses        526     1584     +1058     
- Partials      266      509      +243     

[haircommander]

/lgtm