Add support for fetching SBOMs

[vandanrohatgi]

Closes#2864

Adds support for fetching Software Bill of materials (SBOM) for a repository.

• go generate
• go test
• go vet

[codecov]

Codecov Report

Merging #2869 (c48702b) into master (3ecf12c) will decrease coverage by 0.02%.
Report is 8 commits behind head on master.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #2869 +/- ##
==========================================
- Coverage 98.07% 98.06% -0.02% 
==========================================
Files 139 140 +1 Lines 12348 12269 -79 ==========================================
- Hits 12110 12031 -79 
Misses 162 162 Partials 76 76 

Files Changed	Coverage Δ
github/dependency_graph.go	100.00% <100.00%> (ø)
github/github.go	97.97% <100.00%> (+<0.01%)	⬆️

... and 6 files with indirect coverage changes

[gmlewis]

Thank you, @vandanrohatgi !
Just a couple minor comment nits, please, that I apparently missed the first time
before we await a second LGTM+Approval from any other contributor to this repo before merging.

[vandanrohatgi]

Thank you so much for the valuable feedback @gmlewis ! Learned a lot. Though I feel I only increased your workload rather than contributing :)

[gmlewis]

Thank you so much for the valuable feedback @gmlewis ! Learned a lot. Though I feel I only increased your workload rather than contributing :)

No, not at all, @vandanrohatgi ! Your contributions are appreciated more than you know!
I couldn't maintain this repo without the help of wonderful contributors like yourself.

[gmlewis]

Thank you, @vandanrohatgi !
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[gmlewis]

@Parker77 - do you have time for a code review, please?

[Parker77]

LGTM!

[gmlewis]

Thank you, @Parker77 !
Merging.