Add bitbucketserver_file resource

[Apollorion]

Being able to add files to a git repo is really useful with the terraform github provider. It would be awesome to be able to do the same thing with this provider. I use the github provider to bootstrap repositories with a readme, maybe a generic directory structure, etc. Just as a use-case example.

I'd imagine it would work, something like the github one:
https://registry.terraform.io/providers/integrations/github/latest/docs/resources/repository_file