Installation instructions throwing UnknownPluginException

[Installation](https://github.com/google/secrets-gradle-plugin#installation) calls for adding `com.google.android.libraries.mapsplatform.secrets-gradle-plugin:secrets-gradle-plugin:1.3.0`as a dependency classpath and `com.google.android.libraries.mapsplatform.secrets-gradle-plugin` to `plugins` block, this results in

```bash
Exception is:
org.gradle.api.plugins.UnknownPluginException: Plugin [id: 'com.google.android.libraries.mapsplatform.secrets-gradle-plugin'] was not found in any of the following sources:

- Gradle Core Plugins (plugin is not in 'org.gradle' namespace)
- Plugin Repositories (plugin dependency must include a version number for this source)
```

What has worked for me and is documented [here](https://arriolachris.medium.com/pass-secrets-securely-on-android-1c1d0ec51875) and [here](https://plugins.gradle.org/plugin/com.google.secrets_gradle_plugin) is to add `id "com.google.secrets_gradle_plugin" version "0.6.1"` to the plugins dsl and not adding the dependency classpath.

The installation instructions are included in [Maps SDK Quickstart](https://developers.google.com/maps/documentation/android-sdk/start#add_the_api_key_to_your_app) and don't seem to be working as expected.

To reproduce:
- Install via [Maps SDK Quickstart](https://developers.google.com/maps/documentation/android-sdk/start#add_the_api_key_to_your_app) or [from the repo instructions](https://github.com/google/secrets-gradle-plugin#installation)
- Sync or build your app