Make etcd3 & python-consul2 soft dependencies

[yuvipanda]

Fixes #125

TODO:

• Update docs

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[GeorgianaElena]

Not installing these deps for TraefikToml seems like a good idea 👍 Thanks @yuvipanda!

[GeorgianaElena]

Do you want to add these (etcd3 and python-consul2) to dev-requirements.txt instead, to fix the tests?

[yuvipanda]

That's not a bad idea at all! This is a breaking change tho, so we should announce widely.

I also want to test that the toml provider works without these libraries. How do you think we can do that?

[GeorgianaElena]

I didn't notice any toml proxy test failing in https://github.com/jupyterhub/traefik-proxy/pull/127/checks?check_run_id=2211574725 ❤️ Only the consul and etcd ones.

[yuvipanda]

Right. But in the future, if we accidentally introduce a change that automatically imports etcd3 or python-consul2, the tests in this repo won't catch it! But for an end user who doesn't have these packages installed but only wants to use the TOML proxy, it will fail. So I want to find a way to test that the toml proxy works even without these packages installed.

[dolfinus]

Hello.

Any updates here?

[GeorgianaElena]

Thanks for the ping @dolfinus! This is ready to go, we just need to document the change somewhere visible and add a test to ensure we won't introduce any change in the future that might break TomlProxy when etcd3 and consul clients aren't installed (see @yuvipanda's comment above).

I'll open a new issue about this to un-block this PR.

[dolfinus]

Thanks!