New data source: Mend

[tarkatronic]

🚀 Feature Request

Is your feature request related to a problem? Please describe.

Dependabot may be built in to GitHub and be a great default source of data, but there are a number of competitors, including Mend Renovate, which is very widely used. We should be able to pull in data from there as well.

Describe the solution you'd like

I haven't looked too much into the API but I did find this as a potential starting point: https://docs.mend.io/en-US/bundle/api_sca/page/http_api_v1_3_and_v1_4.html

It would be great to be able to pull in findings from there and present them directly alongside Dependabot findings, in the exact same format. If we can normalize those two... that's amazing. See #47 for that effort.