CODEOWNERS: add self as owner of xpay/askrene/renepay

[Lagrang3]

No description provided.

[daywalker90]

From the CODEOWNERS docs:

A CODEOWNERS file uses a pattern that follows most of the same rules used in [gitignore](https://git-scm.com/docs/gitignore#_pattern_format) files.

Then from gitignore docs:
If there is a separator at the end of the pattern then the pattern will only match directories, otherwise the pattern can match both files and directories.

So you probably want trailing / for your paths.

[ddustin]

ACK 9b866ac