Add new labels for issues related to community repositories

[zakkak]

Feature request

Please add the following new label for issues related to community repositories:

• community-21 (or community-jdk21u if you prefer) to indicate that the issue affects builds based on https://github.com/graalvm/graalvm-community-jdk21u

Is your feature request related to a problem? Please describe. See https://github.com/oracle/graal/discussions/9590

cc @jerboaa @simonis