fix(wikibase): migrate legacy pre-WBS 8 configurations

[lorenjohnson]

Updating to WBS 8 will currently reject a valid LocalSettings.php from an installation upgraded to WBS 7 from an earlier release. Those installations retain the WBS 1–6 inline settings loader rather than the split loader created by fresh WBS 7 installs.

The migration now recognizes both supported pre-WBS-8 layouts, preserves the corresponding settings and anonymous-access behavior, and validates the staged result before installing it. Unrecognized layouts remain unchanged and provide an actionable message with the expected layouts and a support link.

The upgrade tests cover both configuration shapes, formatting and rejection cases, resulting settings, and a rendered MediaWiki page. The WBS 3→4 guide now also makes the required Query Service reindex explicit because that transition changes its index format.

Validation:

• Manual default-install upgrade checks from WBS 1–7 to the WBS 8 candidate:
  • WBS 4–7 reached healthy target service stacks.
  • WBS 1–3 migrated and booted Wikibase successfully; their Query Service stores require the documented reload step after the WBS 3→4 Query Service upgrade.

[github-actions]

Test this PR installer

Use this command instead of the installer command in the published documentation:

curl -fsSL https://wmde.github.io/wikibase-suite-install/pr-983 | bash

This URL tracks the latest successfully published source and image build for this PR.