Add new setup widget UI

[justinbot]

Following #1655 which added support for widgets authenticating with the Provisioning API, this PR adds a new UI for configuring bridged rooms from within a widget:

This is an optional feature, enabled with the Provisioning API:

matrix-appservice-irc/config.sample.yaml

Lines 526 to 528 in bb915f8

	provisioning:
	# True to enable the provisioning HTTP endpoint. Default: false.
	enabled: false

Implementation

At a high level, the widget is just a static webpage which interacts with the Provisioning API to perform configuration.

More specifically, this takes the same approach as the setup widgets in matrix-hookshot, but implemented with the consideration that much of it is generic and could be refactored out into a package for reuse in other bridges.

Provisioning API

This part of the implementation is relevant for any API using the ProvisioningApi class from matrix-appservice-bridge. Includes:

• Parsing widget query parameters.
• Widget API setup and obtaining an OpenID token.
• Exchanging the OpenID token for a session token, storing and checking validity of the session token.
• Instantiating a generic Provisioning API client.

Frontend

The same approach for building a frontend with Vite could be taken for other bridges, as well as the handful of reusable UI components which have been implemented with Tailwindcss.

IRC Bridge

The IRC Provisioning API client and the actual configuration UI are specific to this IRC Bridge.

[Half-Shot]

This is actually looking amazing, you should be very proud of this work! I have a few minor concerns, but the bulk of this is great.

[Half-Shot]

One final thought @justinbot, can you write some documentation on this feature in the hosted docs. It can probably be similar to the hookshot ones. Thanks!

[justinbot]

Sorry about the force push (had to rebase after changes to #1655). New changes start with fe0fabb.

I realized the widget frontend was not actually being linted (and the existing .eslintrc didn't make sense for a frontend app) so I added a separate .eslintrc and fixed a handful of issues it revealed.

And then I took a second pass at the frontend style (see updated screenshot).

[Half-Shot]

Smashing, one note in the docs then this is ready to ship I feel :)

[justinbot]

Rebased one last time following 5f77a70 -- this should be good to go