synctl requires `pid_file` or `worker_pid_file` to be set even when not daemonizing

This issue has been migrated from [#11754](https://github.com/matrix-org/synapse/issues/11754).

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when synctl is run with the `--no-daemonize` flag, synapse will not write a pid file. The `pid_file` and `worker_pid_file` settings in the config are therefore largely redundant; however, synctl still insists on their being present even though they are unused.

Start by tracing synctl's handling of the --no-daemonize flag and its validation of pid_file and worker_pid_file. Confirm the current behavior, then verify that running without either setting succeeds when daemonization is disabled and that pid files remain unnecessary in this mode.

Written by the indexing model from the issue text.