Support copying Canned Responses

[kohlee]

Is your feature request related to a problem? Please describe.
Canned Responses can't be copied and pasted between campaigns like Interaction Step blocks can be.

Describe the solution you'd like
Canned Responses should have a "copy" button, and copied Canned Response blocks should trigger a "paste" button in that section when editing other campaigns.

Describe alternatives you've considered
Previous Canned Responses should be able to be saved to a repository and dragged into a script when editing the Canned Response section in the campaign builder.

Additional context
Other platforms support Canned Response libraries.

[kohlee]

We've received additional requests for a universal Canned Response library.

Option 1: This could live in Settings, and all campaigns could include universal responses when copied or created.
Option 2: When adding a canned response, there could be an option to save to that campaign or save to a universal Canned Response library, editable from within campaigns

[jen-mckinney]

Received an additional request for a Canned Response library.

[hiemanshu]

@politics-rewired/organizing Could we get a fleshed out doc for a Canned Response Library, as part of this issue, and a follow up to #911

[ninabaldwin]

@hiemanshu we have a task for someone to flesh out a design doc!

[ajohn25]

@hiemanshu After further discussion, the "copy" functionality from @kohlee's original description feels most important as a first step. I opened #1550 for the library piece