Depending on the distro, common commands like sleep and chown may either
be located in /bin or /usr/bin.

Systemd added path lookup to ExecStart in v239, allowing only the
command name to be put in unit files and not the full path as
historically required. At least Ubuntu 18.04 LTS is however still on
v237 so we should maintain portability for a while longer.

No migration steps should be required.

This should be a no-op, no migration necessary.

This config change follows:

  https://github.com/turt2live/matrix-dimension/blob/master/docs/unfederated.md

Well, actually 8cd9cde won't work, unless we put the
`|to_nice_yaml` thing on a new line.

We can, but that takes more lines and makes things look uglier.
Using `|to_json` seems good enough.

The whole file is parsed as YAML later on and merged with the
`_extension` variable before being dumped as YAML again in the end.

Fixes #424 (Github Issue).

Some options are no longer required and have sensible default values.

Fixes #403 (Github Issue).

This keeps the roles cleaner and more independent of matrix-base,
which may be important for people building their own playbook
out of the individual roles and not using the matrix-base role.

Regression since #362 (Github Pull Request).

Synapse v1.9.0 changed some things which made the REST Auth Password
Provider break.

The ma1uta/matrix-synapse-rest-password-provider implements some
workarounds for now and will likely deliver a proper fix in the future.

Not much has changed between the 2 projects, so this should be a
painless transition.

Related to #355.