Rollback release 2.1.0b

[pjgg]

There is still an error on the release ci process:

Warning:
Warning: Some problems were encountered while building the effective model for io.quarkiverse.hivemqclient:quarkus-hivemq-client:jar:2.0.1-SNAPSHOT
Warning: 'build.plugins.plugin.(groupId:artifactId)' must be unique but found duplicate declaration of plugin org.apache.maven.plugins:maven-compiler-plugin @ line 83, column 15
Warning: 'build.plugins.plugin.version' for io.quarkus:quarkus-extension-maven-plugin is missing. @ line 56, column 15
Warning:
Warning: It is highly recommended to fix these problems because they threaten the stability of your build.
Warning:
Warning: For this reason, future Maven versions might no longer support building such malformed projects.
Warning:
Error: ] Could not find the selected project in the reactor: docs @
Error: Could not find the selected project in the reactor: docs -> [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/MavenExecutionException
Error: Process completed with exit code 1.

I think that is related to the doc folder. We need to add a pom file to this module.
This PR is rolling back the previous release and adding the missing pom file.