Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3088

Looks like the migration to the Go-based Signal bridge hardcoded the
`signalbot` username instead of using the variable we had.
Related to: https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/3041

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/3089

This is mostly so as to avoid referring to variables from other roles,
like `matrix_nginx_proxy_proxy_matrix_client_api_addr_with_container`.

This should come (and already does) from group_vars/matrix_servers

This also makes it handle the `/_matrix/client/v3/register` endpoint,
not just `/_matrix/client/r0/register`

This reverts commit bf95ad2235.

This was a bad idea.
It's better to have people manually define the password.

Otherwise, `matrix_homeserver_generic_secret_key` changing some day in
the future would break the bot and one would have to figure out how to
reset its password manually.

Using an explicit password is more stable.

* chore(deps): update signal bridge version + config

* style(deps): rename default note to self config variable

* Add to_json for additional safety

---------

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

This is split out from matrix-cactus-comments (see 241779b583),
but also heavily inspired by `matrix-static-files`.

Looks like these variables were originally named this way in
https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2089

Related to https://github.com/mautrix/discord/issues/95

This probably never even worked anyway and was a leftover copy/paste
from some other role.

The docs (`docs/configuring-playbook-bridge-mautrix-wsproxy.md`) only
talk about `matrix_mautrix_wsproxy_hostname`, which was only used via
Traefik labels. The endpoint exposed via `matrix-nginx-proxy` (`/_matrix/wsproxy`)
hasn't been mentioned anywhere.