Version Alignment:
- Updated all plugin dependencies in main Cargo.toml to use 0.15.0
- Changed all plugin Cargo.toml files to use `version.workspace = true`
- Ensured version consistency across the entire workspace

Key Changes:

1. **Workspace Version Inheritance**:
   - All plugins now inherit version from workspace (0.15.0)
   - Replaced individual version numbers with `version.workspace = true`
   - Ensures synchronized versioning across all components

2. **Dependency Updates**:
   - Updated all plugin references in main Cargo.toml to 0.15.0
   - Changed rmqtt-plugins meta-package from 0.1.1 to 0.15.0
   - Maintained consistent versioning pattern

3. **Documentation Updates**:
   - Updated README.md examples to use 0.15.0 for plugin dependencies
   - Changed rmqtt-plugins version from 0.1 to 0.15 in examples
   - Updated individual plugin version references to 0.15

Benefits:
- **Consistent Versioning**: All components now share the same 0.15.0 version
- **Simplified Maintenance**: Single version source in workspace package
- **Better Dependency Management**: Prevents version mismatch issues
- **Clear Release Identity**: Unified version across entire ecosystem

This change ensures that the 0.15.0 release has completely synchronized versions across all components, making dependency management straightforward and preventing potential version conflicts.