Fix Bitbucket GetCommitStatus date parsing

[omerzi]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• I used go fmt ./... for formatting the code before submitting the pull request.
• This feature is included on all supported VCS providers - GitHub, Bitbucket cloud, Bitbucket server, and GitLab.

---

Parsing createdOn and updatedOn values of a commit status failed due to a wrong response parsing.
The Bitbucket server scheme is as follows:

{
    "size": 1,
    "limit": 25,
    "isLastPage": true,
    "values": [
        {
            "state": "SUCCESSFUL",
            "key": "REPO-MASTER",
            "name": "REPO-MASTER-42",
            "url": "https://bamboo.example.com/browse/REPO-MASTER-42",
            "description": "Changes by John Doe",
            "dateAdded": 1442835514204
        }
    ],
    "start": 0
}

The Bitbucket Cloud is as follows:

...
"created_on": "<string>",
"updated_on": "<string>"

In the case of Bitbucket Server, we'll parse the dateAdded field, on Bitbucket Cloud we'll parse the created_on and updated_on fields.

[github-actions]

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