Make ssh connection timeout configurable for offload-build

The following discussion from !234 (merged) should be addressed:

• @anthraxx started a discussion: (+4 comments)

  60s isn't really long enough to cover some user's use cases where they'd want to persist the connection also between multiple builds. Maybe instead we should consider having an ssh_opts function which takes a host and check if the user configured a ControlPersist time (f.e. via ssh -G build.archlinux.org which outputs the config). This way we can provide an opinionated fallback if its undeclared, but preserve user configuration and choices of longer control persist setting.

This was noted as a possible future enhancement and shouldn't be a blocker for merging the related MR! 😅