Add env var to configure local cache path

This adds the option to override the local cache path using an env var.
This is useful to override this in specific environments without
changing the config file.

src/plugins/shadowdog-local-cache.test.ts

@@ -1,5 +1,5 @@
 import fs from 'fs-extra'
-import { describe, it, beforeEach, afterEach, vi, expect } from 'vitest'
+import { describe, it, beforeEach, afterEach, vi, expect, afterAll } from 'vitest'
 import shadowdogLocalCache, { compressArtifact } from './shadowdog-local-cache'
 
 describe('shadowdog local cache', () => {
@@ -117,4 +117,42 @@ describe('shadowdog local cache', () => {
       })
     })
   })
+
+  describe('when local cache path is overriden by env var', () => {
+    beforeEach(async () => {
+      vi.stubEnv('SHADOWDOG_LOCAL_CACHE_PATH', 'tmp/tests/cache_overriden')
+      fs.writeFileSync('tmp/tests/artifacts/foo', 'foo')
+    })
+
+    afterAll(() => {
+      vi.unstubAllEnvs()
+    })
+
+    it('stores the cache in the defined path', async () => {
+      await shadowdogLocalCache.middleware({
+        config: {
+          command: 'echo foo',
+          artifacts: [
+            {
+              output: 'tmp/tests/artifacts/foo',
+            },
+          ],
+          tags: [],
+          workingDirectory: '',
+        },
+        files: [],
+        invalidators: {
+          environment: [],
+          files: [],
+        },
+        next,
+        abort: () => {},
+        options: {
+          path: 'tmp/tests/cache',
+        },
+      })
+      expect(fs.existsSync('tmp/tests/cache/0adeca2ac6.tar.gz')).toBe(false)
+      expect(fs.existsSync('tmp/tests/cache_overriden/0adeca2ac6.tar.gz')).toBe(true)
+    })
+  })
 })

src/plugins/shadowdog-local-cache.ts

@@ -184,6 +184,8 @@ const middleware: Middleware<PluginOptions> = async ({
 
   const mergedOptions = pluginOptionsSchema.parse(options)
 
+  mergedOptions.path = process.env.SHADOWDOG_LOCAL_CACHE_PATH ?? mergedOptions.path
+
   const currentCache = computeCache([...files, ...invalidators.files], invalidators.environment)
 
   fs.mkdirpSync(mergedOptions.path)