Allow to expand limited context lines in a given direction in pull request diff

I/We would want a property to control the amount of lines that get pulled by clicking the expand context button in the pull request diff view.

Expanding diff context lines should be allowed in either upward or downward direction.

The scroll position should be maintained after the context lines have been expanded.

Currently, in Bitbucket Server 7.0 onward, the expand context button will expand all the available lines in both directions, which can lead to multiple thousand lines being shown.