Docs: Add "Configure PostgreSQL Stored Procedure Reaction" page for Drasi Server

[ruokun-niu]

Summary

The Drasi Server Configure Reactions documentation is missing a page for the PostgreSQL Stored Procedure reaction. This reaction ships in Drasi Server but has no how-to guide, so users have no documented way to configure it.

Add a new how-to page documenting the PostgreSQL Stored Procedure reaction, following the structure and style of the existing Drasi Server reaction pages (e.g. the HTTP reaction page).

Background / References

• Reaction kind: storedproc-postgres
• Source implementation: https://github.com/drasi-project/drasi-core/tree/main/components/reactions/storedproc-postgres
• README (primary source for content): https://github.com/drasi-project/drasi-core/blob/main/components/reactions/storedproc-postgres/README.md
• Existing related page (Kubernetes StoredProc reaction, for tone/structure): docs/content/drasi-kubernetes/how-to-guides/configure-reactions/configure-sql-stored-proc-reaction/_index.md

What the reaction does

Invokes PostgreSQL stored procedures when a continuous query's results change. It executes a different, configurable stored procedure for Added, Updated, and Deleted result changes, and maps query result fields into procedure parameters using @after.field / @before.field template syntax. It supports per-query route overrides, a default template, SSL, configurable command timeout, and automatic retries with exponential backoff.

Scope / Tasks

• Create a new page at docs/content/drasi-server/how-to-guides/configuration/configure-reactions/configure-storedproc-postgres-reaction/_index.md.
• Add a card for the new page to the reactions index at docs/content/drasi-server/how-to-guides/configuration/configure-reactions/_index.md (match the existing card-grid pattern).
• Write an intro explaining what the reaction is used for (syncing query result changes into a Postgres database by calling stored procedures for add/update/delete).
• Document the YAML configuration using the Drasi Server config format (kind, id, queries, and plugin fields below).
• Include a configuration reference table for all fields.
• Explain the @after.field / @before.field parameter mapping (added → @after, updated → @after/@before, deleted → @before), including nested-field dot notation.
• Include at least two worked examples (a basic single-query example and a multi-query / per-query routes override example), adapted from the README.
• Include a "Documentation resources" section linking to the README and the crate, matching the pattern used on the HTTP reaction page.

Success Criteria

• New page exists at the path above and renders in the site build without errors (hugo/existing docs build passes).
• The page is linked from the Drasi Server Configure Reactions index page and appears in the card grid.
• Front matter matches the conventions of sibling reaction pages (type, title, linkTitle, weight, description, related).
• All documented config field names, defaults, and the kind value match the source implementation.
• At least one basic example and one routes/multi-query example are present and syntactically valid YAML.
• Parameter mapping (@after / @before) is clearly explained.
• Links to the source README and crate are included and correct.