Add help command to Makefile for improved usability

[nueavv]

Description
This pull request adds a help command to the Makefile, providing users with a clear overview of the available commands and their functionalities.

fixes: #2808

Changes made:

Introduced a help target that outputs the following information in a neatly formatted manner:

Available commands:
  cilium             Build the Cilium binary.
  release            Create a release of the binary.
  local-release      Build binaries for local environment.
  install            Install the Cilium binary.
  clean              Remove the binary and release files.
  test               Run tests with race detection and coverage.
  bench              Run benchmarks.
  check              Run lint checks on the code.
  clean-tags         Remove generated tags and cscope files.
  tags               Generate tags for the source code.

Run 'make <command>' to execute a command.
Use 'make help' to see this help message.

This enhancement improves user experience by making it easier to find and understand the available commands in the Makefile.

[asauber]

Hi @nueavv, thanks for your PR. A couple notes about this change.

Development of the Cilium CLI now happens upstream, in this directory.

https://github.com/cilium/cilium/tree/main/cilium-cli

For active development of the CLI, this help message might be more useful in that context.

The possible confusion here leads me to think that we should consider paring down the makefile in this repo to only the commands that are used by this repo, now that the code has been moved.

With regards to the help message itself, the make targets in this repo are relatively simple, and the risk of the help message becoming innacurate over time, compared to the level of additional information or context that it provides is about equal, so I'm not sure that we need this change.

Given this, I'm going to close this PR for now. Feel free to open it up against the upstream repo to continue the discussion.