Add community SDK section to API docs [Backporting v0.7-branch]

[MichaelHirn]

including reference to community-provided Node.js SDK

What this PR does / why we need it:

"Backports" the original PR #992 into the v0.7-branch so changes get published in the docs.

cc @woop

Which issue(s) this PR fixes:

Does not fix an issue

Does this PR introduce a user-facing change?:

NONE

[feast-ci-bot]

Hi @MichaelHirn. Thanks for your PR.

I'm waiting for a feast-dev member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[MichaelHirn]

/assign @woop

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: MichaelHirn, woop

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