Plugin Architecture Primer

Should be a chapter under https://mariadb.com/docs/server/reference/product-development/plugin-development.

This should provide enough information for people to understand the architecture, e.g. :

• What is a plugin
  • physical package contents
  • types of plugins
  • plugin maturity
  • plugin metadata
  • Server plugin-related inspection tables
• How does the server interact with plugins
  • Inventory of the plugins APIs
• How do plugins interact with the server
  • plugin services
  • functions exposed by the server to plugins
  • calling conventions
• Can plugins interact with each other
• General plugin writing guidelines: e.g.:
  • instrumentation
  • memory management
  • argument data types and handling
  • return values handling etc.
  • lifecycle of plugins within the server
    • INSTALL PLUGIN
    • UNINSTALL PLUGIN
    • Server startup
    • Server shutdown
    • Server upgrade
  • configuration management for plugins
  • status reporting for plugins
• Practical use patterns
  • database-persisted plugin data management (initialization, upgrades, cleanup)
  • SQL execution from within plugin code