feat: rewrite scheduled_tasks in rust

.github/workflows/scheduled_tasks.yml

@@ -1,33 +0,0 @@
-name: Build scheduled tasks runner Docker image
-
-on:
-  push:
-    paths:
-      - .github/workflows/scheduled_tasks.yml
-      - 'services/scheduled_tasks/**'
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    permissions:
-      packages: write
-    if: github.repository == 'PluralKit/PluralKit'
-    steps:
-      - uses: docker/login-action@v1
-        with:
-          registry: ghcr.io
-          username: ${{ github.actor }}
-          password: ${{ secrets.CR_PAT }}
-      - uses: actions/checkout@v2
-      - run: echo "BRANCH_NAME=${GITHUB_REF#refs/heads/}" >> $GITHUB_ENV
-      - uses: docker/build-push-action@v2
-        with:
-          # https://github.com/docker/build-push-action/issues/378
-          context: services/scheduled_tasks/
-          push: true
-          tags: |
-            ghcr.io/pluralkit/scheduled_tasks:${{ env.BRANCH_NAME }}
-            ghcr.io/pluralkit/scheduled_tasks:${{ github.sha }}
-            ghcr.io/pluralkit/scheduled_tasks:latest
-          cache-from: type=registry,ref=ghcr.io/pluralkit/scheduledtasks:${{ env.BRANCH_NAME }}
-          cache-to: type=inline