Update the pipeline to release from tag, run benchmarks

* Extract artifact publishing into a separate job that runs on tag push
* Run benchmarks conditionally on a parameter (currently, must be invoked via API)
* Use a next-generation build image (cimg)

See https://app.circleci.com/pipelines/github/open-toast/protokt/415/workflows/6a8996a3-9aa8-4b84-adbf-a8885103ca13/jobs/461 for a sample execution with benchmarks.

Author: ogolberg

.circleci/config.yml

@@ -1,41 +1,66 @@
 version: 2.1
 
-jobs:
-  build:
+parameters:
+  benchmarks:
+    type: boolean
+    default: false
+
+executors:
+  builder:
     working_directory: ~/code
     docker:
-      - image: circleci/openjdk:11.0.3-jdk-stretch
+      - image: cimg/openjdk:11.0
     environment:
       JAVA_OPTS: "-XX:MaxRAMPercentage=50"
       GRADLE_OPTS: "-Dorg.gradle.daemon=false"
-    steps:
-      - checkout
 
+commands:
+  read_cache:
+    steps:
       - restore_cache:
           key: v1-gradle-wrapper-{{ checksum "gradle/wrapper/gradle-wrapper.properties" }}
       - restore_cache:
           key: v1-gradle-cache-{{ checksum "build.gradle.kts" }}
 
+  write_cache:
+    steps:
+      - save_cache:
+          paths:
+            - ~/.gradle/wrapper
+          key: v1-gradle-wrapper-{{ checksum "gradle/wrapper/gradle-wrapper.properties" }}
+      - save_cache:
+          paths:
+            - ~/.gradle/caches
+          key: v1-gradle-cache-{{ checksum "build.gradle.kts" }}
+
+jobs:
+  build:
+    executor: builder
+    steps:
+      - checkout
+      - read_cache
+
       - run:
-          name: build and test
+          name: Build and test
           command: ./gradlew clean check publishToIntegrationRepository --stacktrace
 
       - run:
-          name: integration tests with kotlin 1.3
+          name: Integration tests with Kotlin 1.3
           command: cd gradle-plugin-integration-test && ./gradlew clean build --stacktrace
 
       - run:
-          name: integration tests with kotlin 1.4
+          name: Integration tests with Kotlin 1.4
           command: cd gradle-plugin-integration-test && ./gradlew clean build -Dkotlin.version=1.4.10 -Dkotlin.api.version=1.4 --stacktrace
+      
+      - when:
+          condition:
+            equal: [ true, << pipeline.parameters.benchmarks >> ]
+          steps:
+            run:
+              name: Benchmarks
+              command: ./gradlew benchmarks:run
 
-      - save_cache:
-          paths:
-            - ~/.gradle/wrapper
-          key: v1-gradle-wrapper-{{ checksum "gradle/wrapper/gradle-wrapper.properties" }}
-      - save_cache:
-          paths:
-            - ~/.gradle/caches
-          key: v1-gradle-cache-{{ checksum "build.gradle.kts" }}
+      - write_cache
 
       - run:
           name: Save test results
@@ -49,13 +74,25 @@ jobs:
       - store_artifacts:
           path: ~/test-results/junit
 
+  
+  release:
+    executor: builder
+    steps:
+      - checkout
+      - read_cache
       - run:
-          name: Deploy (if release)
-          command: "if [[ \"$CIRCLE_BRANCH\" == master ]]; then ./gradlew publishToRemote closeAndReleaseRepository publishPlugins -Dorg.gradle.internal.http.socketTimeout=120000 -Dorg.gradle.internal.network.retry.max.attempts=1 -Dorg.gradle.internal.publish.checksums.insecure=true; else echo skipping publishing; fi"
+          name: Publish release
+          command: "./gradlew publishToRemote closeAndReleaseRepository publishPlugins -Dorg.gradle.internal.http.socketTimeout=120000 -Dorg.gradle.internal.network.retry.max.attempts=1 -Dorg.gradle.internal.publish.checksums.insecure=true"
 
 workflows:
   version: 2.1
   build:
     jobs:
-      - build:
+      - build
+      - release:
           context: OSS
+          filters:
+              tags:
+                only: /^\d+\.\d+\.\d+$/
+              branches:
+                ignore: /.*/