Fix create react admin detect package manager

[djhi]

Problem

create-react-admin does not detect the package manager used to run it correctly.

Solution

Leverage the process.env.npm_config_user_agent environment variable to detect it, just like create-vite

How To Test

Difficult to test without a release as you have to modify the global cache of the package manager.

• For bun it's in $HOME/.bun/install/cache and the package is unzipped into create-react-admin@5.6.0@@@1
• For yarn it's in $HOME/.yarn/berry/cache and the package is not unzipped but renamed to create-react-admin-npm-5.6.0-941ece3bdb-10c0.zip

Additional Checks

• The PR targets master for a bugfix, or next for a feature

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