feat: add allByExternalOwnerIdAndExternalSiteId type to SiteCollection

[radhikagpt1208]

Summary

Adds the missing TypeScript type declaration for allByExternalOwnerIdAndExternalSiteId on the SiteCollection interface in spacecat-shared-data-access.

The runtime method already exists — it is auto-generated from the site schema's external owner/site index (the same index that backs findByExternalOwnerIdAndExternalSiteId). This change only declares the corresponding type so it mirrors the existing findBy... declaration directly above it.

What changed

• src/models/site/index.d.ts — declare allByExternalOwnerIdAndExternalSiteId(externalOwnerId: string, externalSiteId: string): Promise<Site[]> on SiteCollection.

Impact

• Runtime: none — purely a type-declaration change. No behavior change.
• Type-checking: TS consumers can now call the method without casting, and editors provide proper autocomplete.

Test plan

• npm run lint passes.
• Existing unit tests pass (no runtime change).
• Verified the singular findByExternalOwnerIdAndExternalSiteId is already declared and that the plural allBy... accessor is generated from the same index.