Port the third-party event rules interface to the generic module interface introduced in v1.37.0

This adds an API for third-party plugin modules to implement account validity, so they can provide this feature instead of Synapse. The module implementing the current behaviour for this feature can be found at https://github.com/matrix-org/synapse-email-account-validity.

To allow for a smooth transition between the current feature and the new module, hooks have been added to the existing account validity endpoints to allow their behaviours to be overridden by a module.

Our documentation has a history of using a document's name as a way to link to it, such as "See [workers.md]() for details". This makes sense when you're traversing a directory of files, but less sense when the files are abstracted away - as they are on the documentation website.

This PR changes the links to various documentation pages to something that fits better into the surrounding sentence, as you would when making any hyperlink on the web.

By referring to awaitables instead of deferreds.

Fixes #9602

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

* Fix a broken link in the admin api docs

* Rename 10321.doc to 10321.docs

* Rename 10321.docs to 10322.doc

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Fix link in modules doc to point at instructions on registering a callback instead of ones on registering a web resource.

Related to #10251

The presence router docs include some sample homeserver config. At some point we changed the name of the [config option](https://github.com/matrix-org/synapse/blob/859dc05b3692a3672c1a0db8deaaa9274b6aa6f5/docs/sample_config.yaml#L104-L113), but forgot to update the docs.

I've also added `presence.enabled: true` to the example, as that's the new way to enable presence (the `presence_enabled` option has been deprecated).

This PR:

* Converts UPGRADE.rst to markdown and moves the contents into the `docs/` directory.
* Updates the contents of UPGRADE.rst to point to the website instead.
* Updates links around the codebase that point to UPGRADE.rst.

`pandoc` + some manual editing was used to convert from RST to md.

Implemented config option sso.update_profile_information to keep user's display name in sync with the SSO displayname.

Signed-off-by: Johannes Kanefendt <johannes.kanefendt@krzn.de>

This PR adds a common configuration section for all modules (see docs). These modules are then loaded at startup by the homeserver. Modules register their hooks and web resources using the new `register_[...]_callbacks` and `register_web_resource` methods of the module API.

Fixes #9778

ACME v1 has been fully decommissioned for existing installs on June 1st 2021(see https://community.letsencrypt.org/t/end-of-life-plan-for-acmev1/88430/27), so we can now safely remove it from Synapse.

Dangerous actions means deactivating an account, modifying an account
password, or adding a 3PID.

Other actions (deleting devices, uploading keys) can re-use the same UI
auth session if ui_auth.session_timeout is configured.

This doc is short but a useful guide to what the request log lines mean.

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Co-authored-by: Erik Johnston <erik@matrix.org>
Co-authored-by: Daniele Sluijters <daenney@users.noreply.github.com>

* Fix broken links in documentation

* newsfile

This is essentially an implementation of the proposal made at https://hackmd.io/@richvdh/BJYXQMQHO, though the details have ended up looking slightly different.

Signed-off-by: Aaron Raimist <aaron@raim.ist>

With the prior format, 1.33.0 / 1.33.1 / 1.33.2 got separate branches:

    release-v1.33.0
    release-v1.33.1
    release-v1.33.2

Under the new model, all three would share a common branch:

    release-v1.33

As before, RCs and actual releases exist as tags on these branches.

This better reflects our support model, e.g., that the "1.33" series had
a formal release followed by two patches / updates.

Signed-off-by: Dan Callahan <danc@element.io>

Fixes #10121

Signed-off-by: Rohan Sharma <rhnsharma5113@gmail.com>

So that they render nicely in mdbook (see #10086), and so that we no longer have a mix of structured text languages in our documentation (excluding files outside of `docs/`).

Related to: #6681, #5956, #10040

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>

Implements MSC2414: https://github.com/matrix-org/matrix-doc/pull/2414


See #8551 

Signed-off-by: Callum Brown <callum@calcuode.com>

In lieu of just always enabling the unstable spaces endpoint and
unstable room version.

Signed-off-by: Dirk Klimpel <dirk@klimpel.org>