Add Bolt as a Payment Method Option (Solidus 3.0)

[piyushswain]

Summary

This PR adds bolt as a payment method option during solidus installation.

The install_generator.rb file has been updated to add Bolt as an optional payment method during solidus installation. The Bolt option in the payment method installs the solidus_bolt gem.

Ref https://github.com/solidusio-contrib/solidus_bolt/issues/109

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