feat: migrate cookiecutter templates to copier

[kgpayne]

Feature scope

Other

Description

Copier is "A library and CLI app for rendering project templates", similar to cookiecutter but with enhanced support for code lifecycle management (i.e. updating projects as the template changes).

Providing mechanisms for updating Taps/Targets from a single place will allow us to ship new functionality to existing projects using the SDK, drastically reducing the maintenance burden for the community and ourselves (30+ projects in MeltanoLabs).

[kgpayne]

@aaronsteers I had a very brief look at copier, and overall I think it would be a good switch. Some findings:

• Copier uses git under the hood to manage versioning and update diffs, so prefers to have its own git repo per template (e.g. meltano/copier-singer-tap and meltano/copier-singer-target). This means we could feasibly create these repos and test before deprecating the existing cookiecutters.
• Copier also uses jinja for templating, so migrating our existing templates should be straight-forward.

Outstanding questions:

• Is it possible to 'onboard' projects retrospectively? It would be very handy to be able to onboard existing SDK-based Taps/Targets to the new copier templates, so that update would work going forward for those projects.
  • It looks like this might be possible by placing a .copier-answers.yml file in the repo and then calling copier update but it is worth testing this to be sure.

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