Doing this further simplifies examples/vars.yml.

We're trying to move away from implementation-specific variables,
hoping for a clean (implementation-neutral) examples/vars.yml file.

Doing this seems more reasonable and simpler.

- caddy v1 requires a path in the header directive
- msisd has been replaced in favour of ma1sd

Seems to have been added by mistake.

Mostly affects people who disable the integrated `matrix-nginx-proxy`.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/456
and more specifically 4d62a75f6f.

In short, this makes Synapse a 2nd class citizen,
preparing for a future where it's just one-of-many homeserver software
options.

We also no longer have a default Postgres superuser password,
which improves security.

The changelog explains more as to why this was done
and how to proceed from here.

Prompted by this: https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/779#issuecomment-764807507

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/570

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/641

Fixes #685 (Github Issue).

Fixes #586 (Github Issue)

Listen 8448 directive makes apache listen on that port, without it federation does not work.

Invitations weren't working for me until I added 'nocanon' to these additional places. Until then, invitations failed with "Invalid signature for server ..." errors, as in https://github.com/matrix-org/synapse/issues/3294 .

I didn't check whether the user_directory/search proxy line also needs it, I just assumed it should have it too.

The other two proxy lines in this example also include a 'retry=0' parameter. That's a separate issue; I haven't touched it here.

Thanks to @ralfi!

Contributed by @ralfi.