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
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