Add time period parameterization to merge request (PR) visualization endpionts.

[sgoggins]

To have the merge request (PR) endpoints include time period parameterization.

As @ABrain7710 and I discussed, they do not currently, because @sgoggins decided at some point we did not need that for those endpoints. @sgoggins was wrong.

average PR Duration: Not respecting the month parameter. http://spos.osshealth.io:5099/api/unstable/pull_request_reports/Average_PR_duration/?repo_id=25531&remove_outliers=0&group_by=month http://spos.osshealth.io:5099/api/unstable/pull_request_reports/Average_PR_duration/?repo_id=25530&remove_outliers=0&group_by=month http://spos.osshealth.io:5099/api/unstable/pull_request_reports/Average_PR_duration/?repo_id=25158&remove_outliers=0&group_by=month

[aparnaabraham]

Hello, I would like to work on this issue.

[SravaniRaniMishra]

hey, this is my first time in the open source community and i would love to work on this issue. could you please assign it to me