chore: Configure Renovate (#6)

Welcome to [Renovate](https://github.com/renovatebot/renovate)! This is an onboarding PR to help you understand and configure settings before regular Pull Requests begin.

🚦 To activate Renovate, merge this Pull Request. To disable Renovate, simply close this Pull Request unmerged.

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### Detected Package Files

 * `.tool-versions` (asdf)
 * `.drone.yml` (droneci)
 * `mix.exs` (mix)

### Configuration Summary

Based on the default config's presets, Renovate will:

  - Start dependency updates only once this onboarding PR is merged
  - Enable Renovate Dependency Dashboard creation.
  - Use semantic commit type `fix` for dependencies and `chore` for all others if semantic commits are in use.
  - Ignore `node_modules`, `bower_components`, `vendor` and various test/tests directories.
  - Group known monorepo packages together.
  - Use curated list of recommended non-monorepo package groupings.
  - Apply crowd-sourced package replacement rules.
  - Apply crowd-sourced workarounds for known problems with packages.
  - Use semantic prefixes for commit messages and PR titles.
  - Use `chore` as semantic commit type for commit messages and PR titles.
  - Removes rate limit for PR creation per hour.
  - Remove limit for open PRs at any time.
  - Automerge all upgrades (including `major`) if they pass tests.
  - Assign PRs to `james`.
  - Rebase existing PRs any time the base branch has been updated.
  - Raise PR when vulnerability alerts are detected.
  - Disable Renovate Dependency Dashboard creation.

🔡 Would you like to change the way Renovate is upgrading your dependencies? Simply edit the `renovate.json` in this branch with your custom config and the list of Pull Requests in the "What to Expect" section below will be updated the next time Renovate runs.

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### What to Expect

It looks like your repository dependencies are already up-to-date and no Pull Requests will be necessary right away.

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❓ Got questions? Check out Renovate's [Docs](https://docs.renovatebot.com/), particularly the Getting Started section.
If you need any further assistance then you can also [request help here](https://github.com/renovatebot/renovate/discussions).

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This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).

Co-authored-by: Renovate Bot <bot@harton.nz>
Reviewed-on: https://code.harton.nz/james/lex_luthor/pulls/6
Co-authored-by: Renovate Bot <renovate@noreply.localhost>
Co-committed-by: Renovate Bot <renovate@noreply.localhost>

renovate.json

@@ -0,0 +1,6 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "local>renovate/renovate"
+  ]
+}