Bump DiscordRPC plugin to v5

[GeckoEidechse]

Bump DiscordRPC plugin to v5 which corresponds to the first version that supports plugins v3.

See also:

• https://github.com/R2Northstar/NorthstarDiscordRPC/pull/10
• https://github.com/R2Northstar/NorthstarMods/pull/652
• https://github.com/R2Northstar/NorthstarLauncher/pull/472