Increase the function_body_length rule's warning from 120 to 150

[laevandus]

🎯 Goal

We have SwiftLint's warning about function length going on for some time. We either bump the threshold or turn it off completely.

☑️ Contributor Checklist

• [x] I have signed the Stream CLA (required)
• [x] This change follows zero ⚠️ policy (required)
• [ ] This change should be manually QAed
• [ ] Changelog is updated with client-facing changes
• [ ] New code is covered by unit tests
• [ ] Comparison screenshots added for visual changes
• [ ] Affected documentation updated (docusaurus, tutorial, CMS)

🎁 Meme