Small Makefie update

[milosgajdos]

This PR updates Makefile so the default action is help.
We group related targets into semantic groups - this makes the help output easier to read for the end user.

See here:

$ make

Usage:
  make

Build
  bin/%                        build individual binary
  binaries                     build binaries
  build                        build go packages
  image                        build docker image IMAGE_NAME=<name>
  clean                        clean up binaries
  vendor                       update vendor
  mod-outdated                 check outdated dependencies

Test
  test                         run tests, except integration test with test.short
  test-race                    run tests, except integration test with test.short and race
  test-full                    run tests, except integration tests
  integration                  run integration tests
  coverage                     generate coverprofiles from the unit tests

Validate
  lint                         run all linters
  validate                     run all validators
  validate-git                 validate git
  validate-vendor              validate vendor

Go binaries:   bin/registry bin/digest bin/registry-api-descriptor-template
Docker image: distribution/distribution:latest

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (293b588) 57.76% compared to head (d0c0b7b) 57.76%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4018   +/-   ##
=======================================
  Coverage   57.76%   57.76%           
=======================================
  Files         108      108           
  Lines       10500    10500           
=======================================
  Hits         6065     6065           
  Misses       3762     3762           
  Partials      673      673           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[davidspek]

LGTM

[Jamstah]

one nit