Fix https://github.com/element-hq/synapse/issues/18735
In https://github.com/element-hq/synapse/pull/18670, we updated
`run_as_background_process` to add a `server_name` argument. Because
this function is directly exported from the Synapse module API, this is
a breaking change to any downstream Synapse modules that use
`run_as_background_process`.
This PR shims and deprecates the existing
`run_as_background_process(...)` for modules by providing a stub
`server_name` value and introduces a new
`ModuleApi.run_as_background_process(...)` that covers the `server_name`
logic automagically.
31a38f57f5