feat(Schema): whitelist defaultAutoShare boolean configuration key

[WilcoLouwerse]

Summary

• lib/Db/Schema.php::validateConfigurationArray() strips any configuration key not in its allow-list. Adds defaultAutoShare to the $boolFields whitelist so schemas can persist the new key without it being silently dropped on save.
• Also documents the new key in setConfiguration()'s PHPDoc.

Why

Read by the attachment-upload dialog (CnFilesTab in @conduction/nextcloud-vue, and the legacy UploadFiles.vue in opencatalogi) to seed the "Automatically publish" toggle from per-schema configuration. true = toggle on by default; absent / false = off (existing behaviour). Users can always override per upload — the schema value never coerces the submitted share field.

Without this whitelist entry, every PUT that includes configuration.defaultAutoShare returns 200 but the key is dropped server-side, so the consumer never sees the value. Verified by curl -X PUT … -d '{"configuration": {…, "defaultAutoShare": true}}': before this change the response body's configuration object had no defaultAutoShare; after this change it round-trips intact.

Companion PRs

• ConductionNL/nextcloud-vue#455 — CnFilesTab share toggle (active user-facing surface, rendered inside CnObjectSidebar's Files tab)
• ConductionNL/opencatalogi#723 — UploadFiles.vue legacy modal parity + openspec change

Closes ConductionNL/opencatalogi#577 (backend half).

Backward compatibility

• Strictly additive: adds one entry to an existing whitelist. No semantic change for any other key.
• Existing schemas without defaultAutoShare continue to behave exactly as before (validator drop = no key = treated as off downstream).
• No DB migration; the configuration column is already JSON. Existing persisted configs are untouched.

Test plan

• Manual: PUT /api/schemas/{id} with configuration.defaultAutoShare: true — response body now contains the key (verified locally)
• Existing PHPUnit suite passes in CI (this change touches a one-line allow-list; no new tests required unless reviewer prefers one)
• Downstream smoke: with defaultAutoShare: true set on a schema, the CnFilesTab upload dialog seeds the "Automatically publish" toggle on (verifies end-to-end once the nextcloud-vue PR is released)

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