feat: add PLG preonboarding and delivery config backfill scripts

[Kanishkavijay39]

• plg-preonboard.js: preonboards domains by creating org/site, enabling audits and summit-plg, creating ASO entitlement, and setting status to PRE_ONBOARDING so the customer's POST /plg/onboard fast-tracks to ONBOARDED. Resolves canonical URL before RUM lookup to handle www redirects.

• plg-backfill-delivery-config.js: targeted script to backfill deliveryConfig (authorURL, programId, environmentId) for already-preonboarded sites where the initial RUM lookup failed. Uses overrideBaseURL hostname for the RUM query.

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This PR will trigger a minor release when merged.