[DO NOT SQUASH] SCSCANGHA-25 Remove docker and SCSCANGHA-28 Rebranding

[antonioaversa]

This PR contains two tasks:

• SCSCANGHA-25 Replace the Docker action by a composite action forwarding to the SonarQube action
  • implemented as forward to [email protected] (fully-fixed version)
• SCSCANGHA-28 Rebranding
  • Main changes are in the README.md and in the action.yml

We have also added a warning:

• in the README
• in the logs
• in the annotations

Successful test: https://github.com/antonioaversa/dart-tools-test2/actions/runs/12086908914/job/33707231926?pr=1

[antonioaversa]

Given that this action is going to be deprecated, and all it does is to forward to sonarqube-scan-action, I have only kept the tests about the input parameters of the action, which ensure that all the input parameters are forwarded to the sonarqube-scan-action accordingly.
All the other tests are done in the sonarqube-scan-action, including the one on SC Url env var.

[antonioaversa]

Having both dart and light logos with #gh-dark-mode-only and #gh-light-mode-only fragments make the logo responsive to the theme of the user.

[antonioaversa]

All these test files were used by QA workflow tests which now are only executed in the QA of sonarqube-scan-action. So I have removed them.

[antonioaversa]

This is in line with the README of sonarqube-scan-action, except that there are only references to SonarQube Cloud.

[antonioaversa]

Adding @agigleux to validate the warning message (check description in the PR).

[henryju]

LGTM!