Eclipse Theia v1.21.0 Release

Hi everyone :wave:

The Eclipse Theia v1.21.0 release is scheduled for later today, there is still time to merge low-risk pull-requests if necessary.

We will inform you when the release starts.

The release is now ongoing, please do not merge any pull-requests at this time.

The release is now complete, thank you to everyone who contributed :+1: