Publish OLM library on a maven reporsitory

CI of Element Android is regularly broken because Jitpack is not ab le to provide the OLM library.

See for instance https://buildkite.com/matrix-dot-org/element-android/builds/1719

Logs:

Could not determine the dependencies of task ':vector:lintFdroidRelease'.
> Could not resolve all artifacts for configuration ':vector:gplayDebugRuntimeClasspath'.
   > Could not find org.matrix.gitlab.matrix-org:olm:3.2.2.
     Searched in the following locations:
       - https://jitpack.io/org/matrix/gitlab/matrix-org/olm/3.2.2/olm-3.2.2.pom
       - https://oss.sonatype.org/content/repositories/snapshots/org/matrix/gitlab/matrix-org/olm/3.2.2/olm-3.2.2.pom
       - https://github.com/vector-im/jitsi_libre_maven/raw/master/android-sdk-3.1.0/org/matrix/gitlab/matrix-org/olm/3.2.2/olm-3.2.2.pom
       - https://dl.google.com/dl/android/maven2/org/matrix/gitlab/matrix-org/olm/3.2.2/olm-3.2.2.pom
       - https://jcenter.bintray.com/org/matrix/gitlab/matrix-org/olm/3.2.2/olm-3.2.2.pom
     Required by:
         project :vector > project :matrix-sdk-android

It can last a fews days, which is really annoying and can make releases to be postpone.

We should publish the OLM library to an official maven repository, to get ride of the (unidentified so far) issue with Jitpack