🐛 [Sonar] Disabled Sonar Scan for PR/Branches from forks due to missing SONAR_TOKEN not available for forks

[Coduz]

Brief description of the PR.
Disabled Sonar Scan for PR/branches that are from forks.
The SONAR_TOKEN is a secret of the main eclipse-kapua/kapua repo and for security reasons is not available for builds from forks.
Therefore is useless run the Sonar Scan for PR/branches in forks, since the sonar plugin is configured to run with orgname eclipse

The error occurring for all PR from forks is the following

Error:  Failed to execute goal org.sonarsource.scanner.maven:sonar-maven-plugin:5.0.0.4389:sonar (default) on project kapua-assembly-job-engine: Error status returned by url [https://api.sonarcloud.io/analysis/jres?os=linux&arch=x86_64]: 401 -> [Help 1]
Error:  
Error:  To see the full stack trace of the errors, re-run Maven with the -e switch.
Error:  Re-run Maven using the -X switch to enable full debug logging.
Error:  
Error:  For more information about the errors and possible solutions, please read the following articles:
Error:  [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
Error:  
Error:  After correcting the problems, you can resume the build with the command
Error:    mvn <args> -rf :kapua-assembly-job-engine
Error: Process completed with exit code 1.

Related Issue
None

Description of the solution adopted
Added a condition to the run of the Sonar Scan to match only the main eclipse-kapua/kapua repository

Screenshots
None

Any side note on the changes made
None