Restore/save configuration-cache data in first action

Previously, the action was restoring/saving the configuration-cache data for each
step that applied the action. In order to support Gradle invocations that are _not_
managed by the action, the configuration-cache restore is now performed in the initial
action step, and save is performed in the final post-action step.

The build root directories are recorded for each invocation via an init script.

src/main.ts

@@ -1,5 +1,6 @@
 import * as core from '@actions/core'
 import * as path from 'path'
+import * as os from 'os'
 import {parseArgsStringToArgv} from 'string-argv'
 
 import * as caches from './caches'
@@ -14,8 +15,9 @@ export async function run(): Promise<void> {
     try {
         const workspaceDirectory = process.env[`GITHUB_WORKSPACE`] || ''
         const buildRootDirectory = resolveBuildRootDirectory(workspaceDirectory)
+        const gradleUserHome = determineGradleUserHome(buildRootDirectory)
 
-        await caches.restore(buildRootDirectory)
+        await caches.restore(gradleUserHome)
 
         const args: string[] = parseCommandLineArguments()
 
@@ -63,6 +65,15 @@ function resolveBuildRootDirectory(baseDirectory: string): string {
     return resolvedBuildRootDirectory
 }
 
+function determineGradleUserHome(rootDir: string): string {
+    const customGradleUserHome = process.env['GRADLE_USER_HOME']
+    if (customGradleUserHome) {
+        return path.resolve(rootDir, customGradleUserHome)
+    }
+
+    return path.resolve(os.homedir(), '.gradle')
+}
+
 function parseCommandLineArguments(): string[] {
     const input = core.getInput('arguments')
     return parseArgsStringToArgv(input)