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
issue