RELAYMSG support

[Mikaela]

I hope Solanum can implement RELAYMSG for better looking relaybots like Oragono and InspIRCd especially as the IRC world is a bit shaken up due to recent events, which I think may lead into communities dividing over a few networks.

As an example how it looks to users:

[2021-139 15:53:28] <M1kaela/T> /ping
[2021-139 15:53:28] <%R-66Y> pong

• Add draft relaymsg spec ircv3/ircv3-specifications#417

Oragono integrated helpop:

:RELAYMSG <channel> <spoofed nick> :<message>
:
:This command lets channel operators relay messages to their
:channel from other messaging systems using relay bots. The
:spoofed nickname MUST contain a forwardslash.
:
:For example:
:    RELAYMSG #ircv3 Mallory/D :Welp, we linked Discord...
:End of /HELPOP

[hifi]

This would be really handy for low impact bridging of networks. It doesn't provide presence but it's better than having each message visibly coming from a single bot.

[kaniini]

This can be done with m_roleplay module already, can't it?

[singpolyma]

It looks like m_roleplay was removed? #80

[heinrich5991]

Would a PR implementing RELAYMSG be accepted (if it meets code quality standards etc.)?

[dwfreed]

We do not generally implement draft capabilities, so it's not likely at present.