chathistory: Add MSGREFTYPES ISUPPORT token

[progval]

It appears that both Soju and Matrix2051 have issues implementing one of the types (resp. msgid and timestamp).

While they could add full support eventually, these would cause higher resource usage, so it will be beneficial to indicate a preference even if both types are supported.

@emersion and I considered adding optional msgids to read-marker but it would add a lot of complexity to clients, without much benefit.

[syzop]

Yeah, sounds reasonable.

[emersion]

soju patch: https://git.sr.ht/~emersion/soju/commit/c0bbcdcc0af94438cbc9c05578ce2bcb48a84a26

[progval]

and in matrix2051: https://github.com/progval/matrix2051/commit/6c4f8d477654718d8ae534f8eef086c13d452901

[emersion]

And a Goguma patch which disables chathistory when MSGREFTYPES is missing timestamp, because it only supports that at the moment: https://git.sr.ht/~emersion/goguma/commit/5466e6ee58154bdada45baf47b34a4c8d50b87a3