Added resource for bitbucket datacenter integration handling

[peterdeme]

Description of the change

Thanks to @mplushnikov for implementing this in https://github.com/spacelift-io/terraform-provider-spacelift/pull/491

We'll wait for multi vcs to be released before getting this to main.

Type of change

• [ ] Bug fix (non-breaking change that fixes an issue)
• [x] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation (non-breaking change that adds documentation)

Checklists

Development

• [x] Lint rules pass locally
• [x] The code changed/added as part of this pull request has been covered with tests
• [x] All tests related to the changed code pass in development
• [x] Examples for new resources and data sources have been added
• [x] Default values have been documented in the description (e.g., "Dummy: (Boolean) Blah blah. Defaults to false.)
• [x] If the action fails that checks the documentation: Run go generate to make sure the docs are up to date

Code review

• [x] This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• [x] Pull Request is no longer marked as "draft"
• [x] Reviewers have been assigned
• [ ] Changes have been reviewed by at least one other engineer

[truszkowski]

One test is failing. It tries to create a Bitbucket Datacenter default integration, which could be only one. Let's add MultiVCS support first, then this feature, and test creating non-default integration instead of the default one.