Show details Citus query plan instead of just 'Custom Scan'

[RoystonS]

PR is for issue #7885

With Citus installed into Postgres, query plans are augmented to add details of how queries are distributed across shards and worker nodes. But PgAdmin shows these query plans as a single 'Custom Scan ?' query node, hiding all of the plan details:

This PR takes the Citus-enhanced query plans and converts them into a simpler Plan-with-sub-Plans structure that PgAdmin already knows how to render.

The display is largely as demonstrated in PR #7885, but I've tidied it up and added some new icons to represent the various stages better.

Some examples:

A query distributed across 32 nodes, with all 32 tasks appearing in the query plan:

A query distributed across 2 nodes, with only one of the 2 tasks appearing in the query plan, and the Citus distribution appearing in the middle of the overall plan, with aggregation/sorting happening after the Citus distribution:

A problematic query not able to be distributed:

(The text comes directly from the query plan itself, so can't easily be localised in PgAdmin.)

Citus also supports schema-based sharding. This is an example query using that shading scheme:

[Copilot]

Pull Request Overview

This PR enhances PgAdmin's query plan visualization to properly display Citus distributed query plans instead of showing them as generic "Custom Scan" nodes. The changes parse Citus-specific query plan structures and convert them into a format that PgAdmin can render with detailed information about distributed operations.

• Adds parsing logic to handle Citus distributed query plans with Jobs and Tasks
• Implements custom image mapping for Citus-specific node types
• Provides detailed visualization of worker nodes and shard distribution

Reviewed Changes

Copilot reviewed 2 out of 6 changed files in this pull request and generated 3 comments.

File	Description
web/pgadmin/static/js/Explain/index.jsx	Adds parsing logic to convert Citus distributed query structures into standard plan format
web/pgadmin/static/js/Explain/ImageMapper.js	Implements custom image mapping and text formatting for Citus node types

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