ENH Add option to group commits by contributor

[maxime-rainville]

This adds some extra capability to COW so we can generate contribution report for a specific timeframe.

Parent issue

• https://github.com/silverstripeltd/product-issues/issues/814

[maxime-rainville]

This PR also makes it possible to output a table of contribution by members.

Summary

Contributor	Security	API Changes	Features and Enhancements	Bugfixes	Documentation	Merge	Dependencies	Maintenance	Other changes	Total
Maxime Rainville	0	0	0	0	0	0	0	19	0	19
Guy Sartorelli	1	0	7	7	19	0	0	60	0	94
Sabina Talipova	0	0	0	4	0	0	0	1	0	5
sukhwinder-somar	0	0	0	1	0	0	0	0	6	7
dependabot[bot]	0	0	0	0	0	0	18	0	0	18
Sunny Side Up	0	0	0	1	0	0	0	0	0	1
Andrew Paxley	0	0	3	0	1	0	0	0	0	4
github-actions[bot]	0	0	0	0	0	0	1	0	0	1
github-actions	0	0	0	0	0	0	24	0	0	24
Rastislav Brandobur	0	0	0	1	0	0	0	0	0	1
Steve Boyd	0	0	0	1	1	0	0	1	0	3
Ed Wilde	0	0	0	1	0	0	0	0	1	2
Will Rossiter	0	0	0	3	0	0	0	0	0	3
mirche97	0	0	0	0	0	0	0	0	4	4
Bauke Zwaan	0	0	0	1	0	0	0	0	0	1
Nathan J. Brauer	0	0	0	0	0	0	0	0	1	1
Total	1	0	10	20	21	0	43	81	12	188

[GuySartorelli]

I've converted this to draft so that it doesn't accidentally get merged before we've decided we want this in here. As discussed in standup, this doesn't feel like the right place for this.

[GuySartorelli]

Closing since the issue this is linked to was closed.