Port the module to Synapse's pluggable modules

[Iamsomeguy]

Is your feature request related to a problem? Please describe.
The password_providers: module interface has been deprecated and matrix-synapse-ldap3 does not seem to support the new generic module interface.

Describe the solution you'd like
Could you please port the module to the new generic module interface.

Describe alternatives you've considered

Additional context
Here is the error I get if I try to use the module with the generic interface:

2021-11-03 08:37:00,307 - root - 345 - WARNING - main - ***** STARTING SERVER *****
2021-11-03 08:37:00,308 - root - 346 - WARNING - main - Server /opt/venvs/matrix-synapse/lib/python3.7/site-packages/synapse/app/homeserver.py version 1.46.0
2021-11-03 08:37:00,484 - synapse.app._base - 214 - CRITICAL - sentinel - Error during startup
Traceback (most recent call last):
  File "/opt/venvs/matrix-synapse/lib/python3.7/site-packages/synapse/app/_base.py", line 199, in wrapper
    await cb(*args, **kwargs)
  File "/opt/venvs/matrix-synapse/lib/python3.7/site-packages/synapse/app/homeserver.py", line 374, in start
    await _base.start(hs)
  File "/opt/venvs/matrix-synapse/lib/python3.7/site-packages/synapse/app/_base.py", line 390, in start
    module(config=config, api=module_api)
TypeError: __init__() got an unexpected keyword argument 'api'

[reivilibre]

For context:
The password provider module interface was ported to the module API in matrix-org/synapse#10548.

We don't seem to have explicitly called out the deprecation, but it has been removed from the config file and the documentation page for it is deprecated.

Thanks for opening this issue!

[callahad]

@reivilibre has agreed to take a look at this more closely; thank you :)

[richvdh]

handy link: https://matrix-org.github.io/synapse/latest/modules/porting_legacy_module.html

remember to maintain compatibility with the old interface, so as to avoid breaking existing deploys.