chore(scm): fill in get_file and check_file for Bitbucket and Azure DevOps

[cathteng]

Current state of the SCM APIs implemented related to RepositoryMixin:

	check_file	get_file
GitHub	Y	Y
GitHub Enterprise	Y	Y
Gitlab	Y	Y
Bitbucket	Y	N
Bitbucket Server	N	N
Azure DevOps (VSTS)	Y	N

To make the abstraction easier we can fill the rest of these in. Besides Bitbucket Server, the check_file function is already implemented. The difference between check_file and get_file is that we just fully read the file (self.get with raw_response=True), possibly with a slightly different URL, see example implementation in Gitlab:

https://github.com/getsentry/sentry/blob/a0eca661fa254cb6af507d65bee97b1c999dd345/src/sentry/integrations/gitlab/client.py#L310-L327 https://github.com/getsentry/sentry/blob/a0eca661fa254cb6af507d65bee97b1c999dd345/src/sentry/integrations/gitlab/client.py#L329-L344

Notes

• For Bitbucket, the check_file URL already returns the raw file (docs)
• For Bitbucket Server, I referenced this to get the file: -- it seems that you need to add an extra ?raw parameter to fetch the raw file (and another reference to the ?raw part here
• For AzureDevOps, it also looks like the original check_file URL works for get_file. You can add an extra param to download the file but we don't need that (docs)

This PR is useful for https://github.com/getsentry/sentry/pull/74908