docs: google provider page fixes (langchain-ai#18290)

Several URL-s were broken (in the yesterday PR). Like
[Integrations/platforms/google/Document
Loaders](https://python.langchain.com/docs/integrations/platforms/google#document-loaders)
page, Example link to "Document Loaders / Cloud SQL for PostgreSQL" and
most of the new example links in the Document Loaders, Vectorstores,
Memory sections.

- fixed URL-s (manually verified all example links)
- sorted sections in page to follow the "integrations/components" menu
item order.
- fixed several page titles to fix Navbar item order

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Co-authored-by: Erick Friis <erick@langchain.dev>