customgroups 0.9.0 release

This is the server app release template, please copy the part below in a new ticket. For instructions around app releases, see https://confluence.owncloud.com/display/OG/Releasing+Apps

[x] Verify transifex commits (enterprise should update weekly, others daily): If folder l10n exists, then git log should show '[tx] updated from transifex` ...
[x] Ping ProductManagement to check info.xml description and screenshot

[x] Create QA Milestone and set the description to $version
[x] Create release branch with the format "release-$version"
[x] Create "0.9.0 Testplan" --> #619 (QA templates or Enterprise)
[ ] copy new/reopened issues from the previous release ticket as 'Issues to review' below.
[x] check if Non-normal Release Process applies, and adapt this checklist.

[x] Changes in the docs needed? If so create issue in https://github.com/owncloud/docs-server/issues/new .

All actions to be done on the release branch (git pull; git checkout -b release-x.x.x) from here:

[x] Bump version in appinfo/info.xml (no version suffix)
[x] Check php version dependency and minimum ownCloud version dependency in appinfo/info.xml
[x] Bump "sonar.projectVersion=" in sonar-project.properties (no version suffix)
[x] Change CHANGELOG.md 'Unreleased' to '$version' (today's date)

[x] git tag -s v${version}-rc.1 on release branch (see https://confluence.owncloud.com/display/EN/Product+Owners+List)
[x] Build and sign RC tarball from github tag v${version}-rc.1 (see handbook for how to build)
[x] Check buildlog for security reports
[x] Check github security tab dependabot reports
- [ ] -> if critical or high entries are reported: open a release blocker issue.
[x] Upload as Github release using changelog entries
[x] Test and document in testplan + manual explorative testing:
- [ ] If this is an enterprise app: Enabling the app must start the grace period
- [x] Add section "Changlog Testing" using github releases text or CHANGELOG.md from release branch
- [x] Do changelog tests
- [x] Do regression tests
- [x] Watch out for untranslated strings when locale is de oder de_DE.
- [ ] PHP 7.3 compatibility (HCLOUD_SERVER_IMAGE=debian-10 OC10_VERSION=10.11 oc10.sh ...)
- [x] => Final "Go" from QA (set 'QA-ready' label) => else do another RC after fixing issues in the "release-$version" branch

[x] Upload tarball to marketplace (see handbook in confluence for details)
[x] Publish tarball for customers github/owncloud/QA/tools/portal_upload_app.sh - old 10, old 10.0 and new portal (see handbook for details)
[x] Send mail to release-coordination with link to this ticket and to the changelog github/owncloud/QA/tools/release/oc_release.sh app:status
[x] Copy email to rocket chat #updates channel (remove allhttps://` to avoid auto-expansions.)

[x] Add a new 'Unreleased' section in CHANGELOG.md (and also update links at the bottom!)
[x] Create PR to merge changes back to the master branch with description "Closes #XYZ" with the release ticket number
[ ] Rename QA milestone to $version and close the milestone
[ ] Update https://confluence.owncloud.com/display/PROD/Upcoming+Releases
[x] Ensure release template is up to date
[x] Ensure the testplan template (community or enterprise) is up to date
[x] Close the testplan issue

owncloud / customgroups