fix(js): allow pinning importmaps with gem

[mhenrixon]

Since import maps JSPM and the javascript ecosystem are a mess in their current state, allow import maps to match the assets served by the gem rather than download them from JSPM.

pin "@turbo-boost/streams", to: "@turbo-boost/streams.js", preload: false
pin "@turbo-boost/commands", to: "@turbo-boost/commands.js", preload: false
pin "@turbo-boost/elements", to: "@turbo-boost/elements.js", preload: false
pin "alpinejs", preload: false # @3.13.5
pin "@alpinejs/morph", to: "@alpinejs--morph.js", preload: false # @3.13.5

That fixes that problem; I'm happy with this solution for now; seems fair since JSPM never updates. Perhaps we can update the documentation for importmaps to the following:

1. fix(js): allow pinning importmaps with gem turbo_boost-streams#51
2. fix(js): allow pinning importmaps with gem turbo_boost-commands#122
3. fix(js): allow pinning importmaps with gem #49

This is verified to be working with:

gem "turbo_boost-streams",  github: "mhenrixon/turbo_boost-streams"
gem "turbo_boost-commands", github: "mhenrixon/turbo_boost-commands"
gem "turbo_boost-elements", github: "mhenrixon/turbo_boost-elements"