release: Start preparation for 4.15.1

db: use explicit backref definition for sqlalchemy for code analytics not to report errors.

app: dropped deprecated controllers to view_utils which are actually proper name

docs: added release notes for 4.15.1

vcs: streaming will use now 100kb chunks readers for faster throughput

downlaods: properly encode " in the filenames, and add RFC 5987 header for non-ascii files.

audit-logs: add audit logs for API permission calls. - fixes #5490

docs: updated configuration for nginx and reverse proxy.

ops: add better name for anonymous ops/ping calls.

pull-requests: ensure merge response provide more details - refactor merge responses with detailed messages - fixes #5520 - code cleanups