Part of #9744

Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.

`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl&gt;`>

- Merge 'isinstance' calls.
- Remove unnecessary dict call outside of comprehension.
- Use 'sys.exit()' calls.

Fixes #9504

And ensure the consistency of `event_auth_chain_id`.

It used to write an empty file if you gave it a -o arg.

If the script fails (or is CTRL-C'ed) between porting some of the events table and copying of the sequences then the port script will immediately die if run again due to the postgres DB having inconsistencies between sequences and tables.

The fix is to move the porting of sequences to before porting the tables, so that there is never a period where the Postgres DB is inconsistent. To do that we need to change how we port the sequences so that it calculates the values from the SQLite DB rather than the Postgres DB.

Fixes #8619 

Fixes #8618

We do a `SELECT MAX(stream_id) FROM e2e_cross_signing_keys` on startup.

I noticed in https://github.com/matrix-org/synapse/issues/8575 that the `end_error` variable in `synapse_port_db` is set to an `Exception`, even though later we expect it to be a `str`.

This PR simply casts an exception raised to a string. I'm doing this instead of having `end_error` be of type exception as we explicitly set `end_error` to a str here:

https://github.com/matrix-org/synapse/blob/d25eb8f3709965d0face01a041d5292490bf0139/scripts/synapse_port_db#L542-L547

This whole file could probably use some heavy refactoring, but until then at least this fix will prevent exception contents from being hidden from us and users.

This is so we can tell what is going on when things are taking a while to start up.

The main change here is to ensure that transactions that are created during startup get correctly logged like normal transactions.

This table was created in #8034 (1.20.0).  It references
`ui_auth_sessions`, which is ignored, so this one should be too.

Signed-off-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>

The old statement returned `None` for such a `password_config` (like the one
created on first run), thus retrieval of the `pepper` key failed with
`AttributeError`.

Fixes #5315

Signed-off-by: Ivan Vilata i Balaguer <ivan@selidor.net>

* Raise an exception if there are pending background updates

So we return with a non-0 code

* Changelog

* Port synapse_port_db to async/await

* Port update_database to async/await

* Add version string to mocked homeservers

* Remove unused imports

* Convert overseen bits to async/await

* Fixup logging contexts

* Fix imports

* Add a way to print an error without raising an exception

* Incorporate review

Currently we rely on `current_state_events` to figure out what rooms a
user was in and their last membership event in there. However, if the
server leaves the room then the table may be cleaned up and that
information is lost. So lets add a table that separately holds that
information.

We might not need the cursor at all.

* Add a background update to clear tombstoned rooms from the directory

* use the ABC metaclass

I want to do some key rotation, and it is silly that we don't have a way to do
this.

This encapsulates config for a given database and is the way to get new
connections.