[draft]Support configurable file name prefix for blob and file exporters

[Copilot]

This PR adds configurable file name prefix support to blob and file exporters, bringing them in line with the existing S3 exporter functionality. It also renames the S3 environment variable for consistency while maintaining backward compatibility.

Changes Made

1. S3 Exporter Updates

• New: MONOCLE_S3_FILE_PREFIX environment variable (preferred)
• Backward Compatible: Still supports legacy MONOCLE_S3_KEY_PREFIX
• Precedence: New variable takes priority when both are set

2. Azure Blob Exporter Updates

• New: MONOCLE_BLOB_FILE_PREFIX environment variable support
• Fixed: Missing export queue initialization bug

3. File Exporter Updates

• New: MONOCLE_FILE_PREFIX environment variable support
• Behavior: Constructor parameter still takes precedence over environment variable

Environment Variables

Exporter	Environment Variable	Default	Notes
S3	MONOCLE_S3_FILE_PREFIX	monocle_trace_	Preferred over legacy MONOCLE_S3_KEY_PREFIX
Blob	MONOCLE_BLOB_FILE_PREFIX	monocle_trace_	New functionality
File	MONOCLE_FILE_PREFIX	monocle_trace_	Constructor param takes precedence

Usage Examples

# S3 Exporter - new preferred way
os.environ['MONOCLE_S3_FILE_PREFIX'] = 'my_app_traces_'

# Azure Blob Exporter - now configurable  
os.environ['MONOCLE_BLOB_FILE_PREFIX'] = 'azure_traces_'

# File Exporter - now configurable
os.environ['MONOCLE_FILE_PREFIX'] = 'local_traces_'

Testing

Added comprehensive test coverage:

• S3 exporter backward compatibility validation
• Blob exporter prefix configuration tests
• File exporter prefix configuration tests
• Environment variable precedence testing

Backward Compatibility

✅ Fully backward compatible - existing code using MONOCLE_S3_KEY_PREFIX continues to work unchanged.

Fixes #149.

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