RPC: add jamulusserver/setDirectory request to update registration details

[pljones]

What is the current behaviour and why should it be changed?

Currently, whilst the registration status and, if registered, the directory canonical address value can be retrieved using jamulusserver/getServerProfile, there is no method via RPC to change the registration status - e.g. to change to unregistered to set a different directory.

Describe possible approaches

• Introduce jamulusserver/setDirectory taking directoryType and, where directoryType is not "none", directoryAddress.
• Update jamulusserver/getServerProfile to return the values of directoryType and directoryAddress (the latter being directory but without any preprocessing and only assured to be valid when directoryType is custom and registrationStatus is "registered")

Also refactor existing SerializeRegistrationStatus to C++11 std::unordered_map lookup, which will be used to hold the look up tables used for serialising and de-serialising EDirectoryType and ESvrRegStatus values.

Has this feature been discussed and generally agreed?

Discussed in https://github.com/orgs/jamulussoftware/discussions/3510