[Plugin] Code Climate

Signed-off-by: Frank Cycan <frank@hqo.co>

plugins/code-climate/README.md

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+# Code Climate Plugin
+
+The Code Climate Plugin displays a few stats from the quality section from [Code Climate](https://codeclimate.com).
+
+![Code Climate Card](./docs/code-climate-card.png)
+
+## Getting Started
+
+1. Install the Code Climate Plugin:
+
+```bash
+# From your Backstage root directory
+cd packages/app
+yarn add @backstage/plugin-code-climate
+```
+
+2. Add the `EntityCodeClimateCard` to the EntityPage:
+
+```jsx
+// packages/app/src/components/catalog/EntityPage.tsx
+
+import { EntityCodeClimateCard } from '@backstage/plugin-code-climate';
+
+const overviewContent = (
+  <Grid container spacing={3} alignItems="stretch">
+    // ...
+    <Grid item>
+      <EntityCodeClimateCard />
+    </Grid>
+    // ...
+  </Grid>
+);
+```
+
+3. Add the proxy config:
+
+```yaml
+# app-config.yaml
+
+proxy:
+  '/codeclimate/api':
+    target: https://api.codeclimate.com/v1
+    headers:
+      Authorization: Token token=${CODECLIMATE_TOKEN}
+```
+
+4. Create a new API access token (https://codeclimate.com/profile/tokens) and provide `CODECLIMATE_TOKEN` as an env variable.
+
+5. Add the `codeclimate.com/repo-id` annotation to your `catalog-info.yaml` file:
+
+```yaml
+apiVersion: backstage.io/v1alpha1
+kind: Component
+metadata:
+  name: backstage
+  description: |
+    Backstage is an open-source developer portal that puts the developer experience first.
+  annotations:
+    codeclimate.com/repo-id: YOUR_REPO_ID
+spec:
+  type: library
+  owner: CNCF
+  lifecycle: experimental
+```
+
+### Demo Mode
+
+The plugin provides a MockAPI that always returns dummy data instead of talking to the Code Climate backend.
+You can add it by overriding the `codeClimateApiRef`:
+
+```ts
+// packages/app/src/apis.ts
+
+import { createApiFactory } from '@backstage/core-plugin-api';
+import {
+  MockCodeClimateApi,
+  codeClimateApiRef,
+} from '@backstage/plugin-code-climate';
+
+export const apis = [
+  // ...
+
+  createApiFactory(codeClimateApiRef, new MockCodeClimateApi()),
+];
+```