[flagd] Default port to 8015 if in-process resolver is used.

[toddbaert]

The flagd provider defaults to RPC mode and the corresponding port (8013) using the evaluation proto. If the in-process resolver is selected, it operates in in-process mode using the sync proto, but still uses port 8013, instead of defaulting to the correct port (8015, for the sync proto).

We should improve the configuration by defaulting to port 8015 if the in-process resolver is selected.

[zedadyna]

I like to take this one

[thisthat]

Hey @zedadyna, thanks for picking this :) I'm assigning this to you then :)