feat: Add GitHub Actions workflow and action for Vespa CLI

Adds a GitHub Actions workflow to test the Vespa CLI installation using the latest and a specific version of the CLI. Also adds a reusable action to install the Vespa CLI on the runner.

.github/workflows/test.yml

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+---
+name: Test
+
+on:
+  push:
+    branches:
+      - 1.x
+  pull_request:
+    branches:
+      - 1.x
+
+jobs:
+  test:
+    strategy:
+      fail-fast: true
+      matrix:
+        vespa-cli-version: [latest, 8.371.16]
+
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Vespa CLI
+        uses: ./
+        with:
+          version: ${{ matrix.vespa-cli-version }}
+
+      - name: Verify Vespa CLI
+        run: vespa version
+
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Lint YAML files
+        run: yamllint --format github .

.yamllint

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+---
+extends: default
+
+rules:
+  line-length: disable
+  truthy:
+    check-keys: false

README.md

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+# Setup Vespa CLI on GitHub Actions
+
+This action sets up Vespa CLI as part of your GitHub Actions workflow.
+
+## Inputs
+
+| name         | required | type   | default         | description |
+| ------------ | ---      | ------ | --------------- | ----------- |
+| version      | yes      | string | `latest`        | The version of Vespa CLI to install. |
+
+## Example usage
+
+Workflow:
+
+```yml
+---
+name: CI
+on:
+  push: ~
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Install Vespa CLI
+      uses: vespa-engine/setup-vespa-cli@v1
+
+    - name: Do something with the vespa CLI
+      run: |
+        vespa auth login
+        ...
+        vespa deploy
+
+```

action.yml

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+---
+name: "Setup Vespa CLI"
+description: "Installs the Vespa CLI tool on the runner."
+
+inputs:
+  # The version of the Vespa CLI to install.
+  version:
+    description: "The version of the Vespa CLI to install."
+    default: "latest"
+
+runs:
+  using: "composite"
+  steps:
+    - name: Select CLI version
+      shell: bash
+      id: vespa-cli-version
+      run: |
+        if [ "${{ inputs.version }}" == "latest" ]; then
+          VESPA_CLI_VERSION=$(curl -fsSL https://api.github.com/repos/vespa-engine/vespa/releases/latest | jq -r '.tag_name' | sed 's/^v//')
+        else
+          VESPA_CLI_VERSION="${{ inputs.version }}"
+        fi
+
+        echo "version=${VESPA_CLI_VERSION}" >> "$GITHUB_OUTPUT"
+
+    - name: Install Vespa CLI
+      shell: bash
+      env:
+        VESPA_CLI_VERSION: ${{ steps.vespa-cli-version.outputs.version }}
+        ARCH: ${{ startswith(runner.arch, 'ARM') && 'arm64' || 'amd64' }}
+      run: |
+        ARCHIVE_NAME="$(echo "vespa-cli_${VESPA_CLI_VERSION}_linux_${ARCH}" | tr '[:upper:]' '[:lower:]')"
+        DOWNLOAD_URL="https://github.com/vespa-engine/vespa/releases/download/v${VESPA_CLI_VERSION}/${ARCHIVE_NAME}.tar.gz"
+        echo "Downloading: ${DOWNLOAD_URL}"
+
+        curl -fsSL "${DOWNLOAD_URL}" | tar -zxf - -C /opt
+
+        chmod +x /opt/${ARCHIVE_NAME}/bin/*
+        ln -sf /opt/${ARCHIVE_NAME}/bin/vespa /usr/local/bin/
+
+        # Verify the installation
+        vespa version