Trimming for long-term storage

[therealryan]

This project has a few wee bits that need tiny amounts of regular attention:

• Dependabot will create a bunch of PRs to update dependencies every Monday morning - these need to be manually reviewed and approved/rejected as appropriate
• We use an instance of bowlby to avoid dealing with build artifact zips, but that instance runs on external infrastructure with perishable components (SSL certs, API access token, the VM)

This PR preps the project for periods of low maintenance capacity by:

• Deleting the dependabot config. Our dependencies will go stale, but that's better than having really boring PRs stacking up.
• Dropping usage of the bowlby instance. We're then stuck downloading zips like savages, but that's better than having dead links.

#968 is the other half of this, and should be merged at the same time.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud