Fixes https://github.com/twentyhq/core-team-issues/issues/1956
**Problem**
Within an app, the `.yarn/releases/` folder contains executable Yarn
binaries that run when executing any yarn command (`.yarnrc` file
indicates yarn path to be `.yarn/releases/yarn-4.9.2.cjs `.)
This is a supply chain attack vector: a malicious actor could submit a
PR with a compromised `yarn-4.9.2.cjs binary`, which would execute
arbitrary code on developers' machines or CI systems.
**Fix**
Actually, thanks to Corepack, we don't need to store and execute this
binary.
Corepack can be seen as the manager of a package manager: in
`package.json` we indicate a packageManager version like
`"packageManager": "yarn@4.9.2"`, and when executing `yarn` Corepack
will securely fetch the verified version from npm, avoiding the risk of
executing a compromised binary committed to the repository. This was
already in our app's package.json template but we were not using it!
We can now
- remove the folder containing the binary from our app template
base-application (that is scaffolded when creating an app through cli),
`.yarn/releases/`, and remove `yarnPath: .yarn/releases/yarn-4.9.2.cjs`
from its .yarnrc
- remove them from the community apps that were already published in the
repo
- add .yarn to gitignore
**Tested**
This has been tested and works for app created in the repo, outside the
repo, and existing apps in the repo
