fixup: Simplify nix installation with a custom action

.github/actions/install-nix/action.yml

@@ -0,0 +1,17 @@
+name: 'Install nix'
+description: 'Install nix and populate the store for the repo flake'
+
+inputs:
+  github_token:
+    description: "github token to authenticate with to avoid being rate-limited"
+    default: ${{ github.token }}
+    required: false
+
+runs:
+  using: composite
+  steps:
+    - uses: cachix/install-nix-action@v30
+      with:
+        github_access_token: ${{ inputs.github_token }}
+    - run: nix develop --command echo "dependencies installed"
+      shell: bash

.github/actions/run-monitored-tmpnet-cmd/action.yml

@@ -41,6 +41,9 @@ inputs:
 runs:
   using: composite
   steps:
+    # Ensure promtail and prometheus are available
+    - name: Install nix
+      uses: ./.github/actions/install-nix
     - name: Start prometheus
       # Only run for the original repo; a forked repo won't have access to the monitoring credentials
       if: (inputs.prometheus_username != '')

.github/workflows/ci.yml

@@ -51,11 +51,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: ./.github/actions/setup-go-for-project
-      - uses: cachix/install-nix-action@v30
-        with:
-          github_access_token: ${{ secrets.GITHUB_TOKEN }}
-      # TODO(marun) Maybe figure out how to use `nix build` somehow i.e. make the default shell double as the default package
-      - run: nix develop --command echo "dependencies installed"
       - name: Build AvalancheGo Binary
         shell: bash
         run: ./scripts/build.sh -r
@@ -75,10 +70,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: ./.github/actions/setup-go-for-project
-      - uses: cachix/install-nix-action@v30
-        with:
-          github_access_token: ${{ secrets.GITHUB_TOKEN }}
-      - run: nix develop --command echo "dependencies installed"
       - name: Build AvalancheGo Binary
         shell: bash
         run: ./scripts/build.sh -r
@@ -97,10 +88,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: ./.github/actions/setup-go-for-project
-      - uses: cachix/install-nix-action@v30
-        with:
-          github_access_token: ${{ secrets.GITHUB_TOKEN }}
-      - run: nix develop --command echo "dependencies installed"
       - name: Build AvalancheGo Binary
         shell: bash
         run: ./scripts/build.sh
@@ -233,9 +220,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: ./.github/actions/setup-go-for-project
-      - uses: cachix/install-nix-action@v30
-        with:
-          github_access_token: ${{ secrets.GITHUB_TOKEN }}
+      - uses: ./.github/actions/install-nix
       - run: nix develop --command echo "dependencies installed"
       - name: Run e2e tests
         shell: bash