allow for pull requests to require approval (BB-6920)

We would like to modify our workflow to require that a pull request requires as least two approvals from the team in order to merge into our master tree. Is this is already possible with bitbucket?

Obviously we can simply tell our project leads not to accept a pull request until two approvals show up, but we try to maintain a team-based mentality where no single member has totalitarian control. Having said that, it is sometimes difficult to ensure that every single change that makes it in has indeed been reviewed by multiple parties.