docs: Add troubleshooting docs

[jeanduplessis]

Description of your changes

Adds troubleshooting info that was previously available in the https://github.com/upbound/provider-terraform repo (no longer accessible) covering:

1. Problem Description: Clear explanation of reconciliation blocking issues
2. Root Cause Analysis: Deep dive into the RWMutex locking mechanism that causes the blocking
3. Solutions & Workarounds:
   - Persistent volume mounting (recommended solution)
   - Plugin cache disabling for high concurrency
   - Optimized concurrency settings
4. Monitoring & Diagnosis: Prometheus queries for tracking performance
5. Remote Git Repository Issues: Additional context on git-backed workspace limitations
6. Error Messages & Recovery: Common error patterns and resolutions
7. Best Practices: Production deployment recommendations

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.

How has this code been tested

n/a