Move @electron/rebuild into optionalDependencies

Pre-flight checklist

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• I agree to follow the code of conduct that this project uses.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Problem description

Many firms disallow installation of node-gyp. This module is dragged in through @electron/rebuild, thus preventing @electron/forge from being installed without hacky workarounds.

I believe this problem can be solved by moving @electron/rebuild into optionalDependencies. Only a small percentage of electron projects require native module building, and those projects almost by definition won't have restrictions on node-gyp. Anyone else will be able to install the library without getting stuck at this point.

Proposed solution

Move @electron/rebuild into optionalDependencies.

Alternatives considered

To get around this problem, we've been using a resolution that points node-gyp to a fake library. But this requires some manual hand-holding with our customers.

Additional information

No response