Add changelog for 506
This MR was automatically created from CI, https://gitlab.com/gitlab-org/gitter/gitter-android-app/-/jobs/718990386
We moved CURRENT_VERSION.txt
-> 506.txt
This MR was automatically created from CI, https://gitlab.com/gitlab-org/gitter/gitter-android-app/-/jobs/718990386
We moved CURRENT_VERSION.txt
-> 506.txt