Upstream release notes

https://docs.pagure.org/copr.copr/release-notes/2020-12-01.html

copr-backend

• incremental createrepo is fast again (fixed regression)
• drop call to stomp.conn.start(), new stomp dropped this long time ago
• the request re-tries for frontend moved to python3-copr-common

copr-frontend

• added new --isolation per-project/build options
• several smaller bugfixes

copr-rpmbuild

• the --isolation option implemented
• the builder now repeatedly tries to communicate with frontend (in case of it is offline)