Add lines of code changed over time to charts page

Problem to solve

After the commit graphs have been consolidated and redesigned in https://gitlab.com/gitlab-org/gitlab-ce/issues/51567, we should add additional metrics that repo owners would find helpful.

One such perspective is breaking commits down further into LOC and presenting additions/deletions over time.

Proposal

• Show a chart of additions and deletions over time, based on lines of code.
  • This should be based off master.

Links / references