Support selecting new visits per-request

[DiamondJoseph]

#305 adds a DirectoryProvider implementation which is capable of mounting a single static visit per-beamline. All devices are configured to write to that visit directory, and a pre-processor may be used to update the dataCollection ("dcid") such that files are uniquely named (e.g. --.h5, with dcid incrementing with each run. The visit may be updated by updating the dodal module and restarting the process. This is sufficient for current single-visit development and runs.

When a more complete DirectoryService has been created, and authentication information can be passed as part of the request, it should be possible to select a visit per-request.

If the DirectoryService also produces a subdirectory within the visit per-datacollection, the resource_dir can also be extended to write the h5 files within.

Acceptance Criteria

• Multiple Runs can be started, each writing into a different visit directory on the same beamline without restarting the process.