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[bot]]

[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](https://github.com/containers/conmon-rs/blob/main/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]

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

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Additional details and impacted files

```diff @@ 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