Including another batch of fixes to the schema dump script

* Generate separate snapshots for sqlite, postgres and common
* Cleanup postgres dbs in the TRAP
* Say which logical DB we're applying updates to
* Run background updates on the state DB
* Add new option for accepting a SCHEMA_NUMBER

* Two scripts are basically entry_points already
* Move and rename scripts/* to synapse/_scripts/*.py
* Delete sync_room_to_group.pl
* Expose entry points in setup.py
* Update linter script and config
* Fixup scripts & docs mentioning scripts that moved

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

Signed-off-by: Nick Barrett <nick@beeper.com>

On NixOS, `bash` isn't under `/bin/bash` but rather in some directory in `$PATH`. Locally, I've been patching those scripts to make them work.

`/usr/bin/env` seems to be the only [portable way](https://unix.stackexchange.com/questions/29608/why-is-it-better-to-use-usr-bin-env-name-instead-of-path-to-name-as-my

) to use binaries from the PATH as interpreters.

Signed-off-by: Quentin Gliech <quentingliech@gmail.com>

Remove conflicting sqlite tables that throw sqlite3.OperationalError: object name reserved for internal use: event_search_content when running the twisted unit tests.

Fix #8996