[WIP] Add docs for the assign/unassign entity group to edge rule nodes

[AndriiLandiak]

Description

Documents the two new PE rule nodes added in thingsboard/thingsboard-pe#5030: assign entity group to edge and unassign entity group from edge.

Both nodes ship with a docUrl pointing at these pages, so until this lands the in-form help button 404s for both.

In PE an entity group is the only route by which devices, assets, entity views, dashboards and users reach an edge, so these nodes are what let a rule chain automate edge onboarding instead of doing it by hand.

Each page follows the add-to-group layout — configuration, message processing algorithm, output connections, worked examples with real config JSON, and a JSON schema — plus a ## Usage section (the rest-call-reply precedent) covering how to actually wire the node into a chain:

• the three ways to get an edge name into the message for Edge name pattern mode, and why only one of them needs a script node
• guarding the node with check fields presence, and why an unresolved pattern is a Failure rather than a silent skip
• handling both edge-resolution modes in one chain via entity type switch
• why this node belongs on a provisioning path rather than on raw telemetry

Type of change

• New / updated documentation page (src/content/docs/**)
• Shared include file (src/content/_includes/**)
• Component, layout, or styling change (src/components/**, src/styles/**)
• Landing / use-case / case-study page (src/pages/**, src/data/**)
• Redirects (public/redirects.json regenerated — see note below)
• Version bump / release (see release skill)
• Build, CI, scripts, or tooling
• Other (please describe)

Affected products

The nodes are PE features, so PE and PaaS (including the EU variant) are the pages that matter. Stubs are added for all six product variants — CE, PE, PaaS, PaaS EU, Edge, Edge PE — because every other action node has all six, and the shared include carries the "requires ThingsBoard PE or ThingsBoard Cloud" note rather than the stub set being trimmed.

Related issues

Platform side: thingsboard/thingsboard-pe#5030. No tracking issue.

Note on redirects

src/data/redirects.ts is unchanged — nothing was renamed or removed. public/redirects.json is regenerated because the generator enumerates every page under the user-guide/rule-engine-2-0/nodes/* → reference/rule-engine/nodes/* prefix rename, so two new pages add ten entries (four product prefixes, plus the pe/edge → edge/pe rename).

Worth knowing for the platform PR: both nodes' docUrl values use the legacy user-guide/rule-engine-2-0/... shape, matching the shipped add-to-group and remove-from-group nodes. That resolves through the splat rule in public/_redirects, so no annotation change is needed on the platform side.

Checklist

• pnpm check passes — 0 errors, 0 warnings across 646 files
• pnpm lint:eslint passes
• pnpm lint:slugcheck passes
• pnpm lint:linkcheck passes locally — run against a full pnpm build:fast (4535 pages), no link issues
• Redirects regenerated with pnpm generate:redirects
• No hardcoded versions
• Screenshots attached for visual changes — n/a, content only, no component or style changes