Feature Request: Enable corepack by default

**Describe the Feature Request**
Enable corepack by default

**Is your feature request related to a particular problem?**
The version of yarn in the image is v1. The recommended way to install latest versions of yarn is via corepack. Corepack is not enabled so you need to add an extra `sudo corepack enable yarn` in each job you run a yarn command.

See more:
- https://yarnpkg.com/getting-started/install
- https://yarnpkg.com/corepack

**How will this feature request benefit CircleCI jobs using this image?**
It will allow users to install yarn in the recommended fashion and remove extra command they need to run in each job. It also will allow users to de-duplicate package manager version info.

**Describe the solution you would like to see**
Corepack should be enabled by default. Running `yarn` should use the version specified in the `package.json` `packageManager` property.

**Describe alternatives you have considered**
- `npm i -g yarn@[my-version]`
- `sudo corepack enable yarn@[my-version]`