add dependabot to image builder repo

[nawazkh]

Change description

• This PR adds dependabot to image-builder repo.

Related issues

Additional context

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[nawazkh]

Not sure if I am missing any context on why dependabot was not added to this repo, so creating this PR to add it.

[nawazkh]

/cc @mboersma @jsturtevant @jackfrancis

[AverageMarcus]

There's some background context in this issue: #1283

Could you please include examples of what updates dependabot will generate for us? What versions will be covered, what wont?

[nawazkh]

Thank you for sharing the context @AverageMarcus. It is an interesting challenge to update various hardcoded semver-versions along with dependabot version updates.

I have an idea, not sure how viable, but here it is: (I will mark this PR draft to avoid notification churn)

• Configure dependabot to update versions in package-manager. In our case, say Dependabot updates a dependency in Dockerfile.
• Have a script that scans all the dirs for below files and find dependencies variables, replace them with latest version in the same Dependabot's PR(this can be achieved using GitHub actions).
  • *.json
  • .hcl
  • *.sh

Marking this PR WIP and push changes soon. Thanks!