fsmonitor: add support for extra `hg debuginstall` data This might make some things easier to debug, and for default bug report templates it'll help collect more data from users all at once. I don't actually need fsmonitor in our bug reports (we don't use it), but this demonstrates the utility of the preceding patches without having to add new things to core. Differential Revision: https://phab.mercurial-scm.org/D6682