Update pgvector docs to include Go (using weave)

[ssbushi]

Checklist (if applicable):

• Docs updated

[ssbushi]

I want to include more than just the code for defining a retriever (eg: the right imports). But using %include consecutively generates multiple code blocks in the markdown file. I opted to keep it simple

[kevinthecheung]

This won't render correctly with markdown embedded within the HTML. Could you please put these files in docs-go instead? (Just the go version.) I will combine everything all at once when go graduates out of alpha

[ssbushi]

@kevinthecheung Moved the go snippets to docs-go. PTAL

[kevinthecheung]

Thank you!