[ThreatMatch] - Fixed HTML Parsing, fixed errors with relationships, various bug fixes

[pietrocapece]

Proposed changes

• Fixed HTML parsing
• Fixed bugs with relationships not correctly being ingested
• Cleaned code

Related issues

• https://github.com/OpenCTI-Platform/connectors/issues/4110

Checklist

• [X] I consider the submitted work as finished
• [X] I have signed my commits using GPG key.
• [X] I tested the code for its functionality using different use cases
• [X] I added/update the relevant documentation (either on github or on notion)
• [X] Where necessary I refactored code to improve the overall quality

Further comments