Add option to remove --- _Created from_ [_Atlassian for VS Code_] message in PR messages

[Jake Wilson]

The extension automatically includes the following text in every Bitbucket PR message:

‌

--
_Created from_ [_Atlassian for VS Code_](https://marketplace.visualstudio.com/items?itemName=Atlassian.atlascode))

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Please add the option to either customize this messaging or to remove it completely. My company has strict commit and PR message structure requirements and having unexpected text like this in the messaging is a problem. I have to manually delete it each time.

[Jonathan Doklovic]

Linked to VSCODE-1168