Rebrand to restrict-imports-plugin

[skuzzle]

The repository name and group ids of published artifacts should be rebranded to reflect that we now also have a gradle plugin.
Proposal:

• Repository name: restrict-imports-plugin
• Enforcer Plugin: de.skuzzle.restrict.imports.maven:restrict-imports-enforcer-rule
• Gradle Plugin: de.skuzzle.restrict.imports.gradle:restrict-imports-gradle-plugin
• Gradle Plugin ID: de.skuzzle.restrict.imports

Maybe we should publish the enforcer with the old coordinates as well, so that users are able to get automatic update via Dependabot/Renovate.
The version published with old coordinates should print a deprecation warning so that we can remove the extra publication with the next major version