Add comprehensive wait events coverage gap analysis

[NikolayS]

This analysis identifies 92 specific code locations across PostgreSQL where operations may block or consume significant time without proper wait event instrumentation, causing monitoring tools to incorrectly show activity as "CPU" load.

Key findings:

• 35 critical I/O operations (fsync, stat, unlink, directory ops)
• 20 authentication operations (LDAP, DNS, ident, RADIUS, SCRAM)
• 6 compression operations (gzip, LZ4, Zstandard in base backup)
• 5 cryptographic operations (SCRAM auth, SQL hash functions)
• 6 executor operations (hash joins, aggregates without interruption)
• 9 maintenance operations (vacuum, analyze, sorting)
• 10 logical replication operations
• Various other synchronization and buffer management issues

The report includes:

• Detailed code locations with file paths and line numbers
• Impact assessment for each category
• Proposed new wait events (~40-50 new events)
• Implementation roadmap in 5 phases
• Cost-benefit analysis

Estimated impact: This work could eliminate 70-80% of "CPU*" false positives in monitoring tools, providing accurate visibility into what PostgreSQL is actually doing.