Check on implementing dependabot

[machallboyd]

Following PR https://github.com/NREL/mappymatch/pull/140, we've got requirements defined suitable for installation with pip, with a version-pinned set of test requirements in requirements.txt. We should theoretically be able to use dependabot to generate PRs to bump pinned requirements automatically, which, combined with the CI tests, should tell us if an upgraded dependency has broken something.