Allow for custom npm packages in imported protos

[jasonbrown-alis]

Here is a link to the line where it speaks to our issue.

protobuf-javascript/generator/js_generator.cc

Lines 116 to 119 in 6113588

	// Well-known types (.proto files in the google/protobuf directory) are
	// assumed to come from the 'google-protobuf' npm package. We may want to
	// generalize this exception later by letting others put generated code in
	// their own npm packages.

We currently make use of a variety of google protos other than those in the google-protobuf npm package. To make use of these, we have to explicitly include them in the npm package that we publish containing our generated protobufs. It would be ideal if we could publish the generated google protobufs we use in a separate npm package and use options in the .proto files to specify the name of the package to which these are published, and for this package to be used in the generated code whenever one of these protobufs is implemeneted. Similar to how this is for the "google-protobuf" imports

[dibenede]

From triage: We should consider doing this to make things easier for folks.