feat: Add MySQL 8.4-specific replication and connection templates

[renecannao]

Summary

Add dedicated templates for MySQL 8.4+ that account for syntax and variable changes from 8.0.

Motivation

MySQL 8.4 changed several replication-related variable names and defaults compared to 8.0:

• CHANGE MASTER TO → CHANGE REPLICATION SOURCE TO
• SHOW SLAVE STATUS → SHOW REPLICA STATUS
• Crash-safe replication options differ
• Connection info SQL differs
• Group replication variable names changed

While our current templates work (we fixed the critical compat issues), having dedicated 8.4+ templates would produce cleaner output and avoid deprecation warnings.

Requirements

• init_slaves_84.gotxt — replication init using 8.4+ syntax
• repl_crash_safe_options84.gotxt — 8.4-compatible crash-safe options
• group_repl_options84.gotxt — 8.4-compatible group replication options
• connection_info_sql_84.gotxt — connection info using 8.4+ system variables
• Template selection logic: use 8.4+ templates when version >= 8.4
• load_grants_cluster.gotxt — grants template for cluster topology

Implementation Notes

• Add version-checking logic in template selection (existing capabilities.go can be used)
• Keep backward compatibility with 8.0 templates
• PXC 8.4 may also need dedicated templates (pxc_replication57.gotxt pattern)

[coderabbitai]

🔗 Related PRs

#19 - Drop MySQL 4.1/5.0/5.1 support, add 8.4/9.x to supported versions [merged]
#22 - Add MySQL integration tests (8.0, 8.4, 9.1) [merged]
#23 - Fix remaining templates for MySQL 8.4+ replication syntax [merged]

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