feat: subdomain takeover scanner

[lcampbell2]

MVP 1

• takes in dns_scanner_results from NATS
• Uses fingerprint data from https://github.com/EdOverflow/can-i-take-over-xyz
• Process if subdomain is vulnerable to DNS (CNAME, NS) hijacking
• writes findings to DB with evidence, confidence level, and remediation guidance
• add value to domain documents for quick look-ups

MVP 2

• add filters for subdomain takeovers
• expose to auth'd users on api
• add frontend views