Add Go and Javascript SDKs to docs; Expand Python & Java guides

[akeller]

Describe what's missing in our docs

Based on https://github.com/kestra-io/client-sdk, it looks like Go and Javascript need to be added to the docs. I assume both of these are officially supported SDKs as well.

AJ Edit: Let's also mention that, with the maturity of the SDKs, we expand these to be more than merely method references, but complete guides.

[wrussell1999]

100%. We also need to add more info on the SDKs. They only got added a few months ago but there's little guidance on using them at the moment too.

[aj-emerich]

They are not yet officially supported and have been intentionally left out of the documentation, as the versions currently available in that repository will undergo many breaking changes. JS should be a part of the 1.2 release, and Go (re)development work started today.

I'll assign myself to avoid external contributors jumping onto this and making a doc for a bugged feature 😄

[aj-emerich]

As for Will's comment, they are currently just reference documents for the primary methods. As they mature, we can make some additional guide content. The SDK has been a bit flaky, so in the interest of maintenance, these simple reference documents help us avoid having to update too many things. This issue can serve as our tracking for building this feature out more content-wise.