add -p/--slippi-port cmd line option for spectate server port

[jmlee337]

fixes #419

this will allow developers to connect to the spectate server on multiple dolphin instances on the same machine

[NikhilNarayana]

apologies for suddenly changing my mind, i re-read it and decided i'd rather have this be very explicit about what port it refers to

[jmlee337]

looks like there's a precedent for 'slippi spectate' as in SlippiSpectateServer:

Ishiiruka/Source/Core/Core/Slippi/SlippiSpectate.h

Line 39 in a9c5519

class SlippiSpectateServer

is this ok?

[NikhilNarayana]

looks like there's a precedent for 'slippi spectate' as in SlippiSpectateServer:

Ishiiruka/Source/Core/Core/Slippi/SlippiSpectate.h

Line 39 in a9c5519

class SlippiSpectateServer

is this ok?

not necessarily against it, but i would like the corresponding config value to be renamed to match so it is easy to match them up, if you prefer just spectate

[jmlee337]

oh the config name lol oops. No I'll go spectator I don't want to change the config name that could be breaking if people are touching it programmatically