1. Avoid losing plugin if plugin failed to load when replaying
When in replay process, the plugin should always be added to the plugin manager,
even if that plugin failed to be loaded.
2. `show plugin` statement should show all plugins, not only the successfully installed plugins.
3. plugin's name should be unique globally and case insensitive.
4. Avoid creating new instances of plugins when doing metadata checkpoint.
5. Add a __builtin_ prefix for builtin plugins.
Currently we have implemented the plugin framework in FE.
This CL make the original audit log logic pluggable.
The following classes are mainly implemented:
1. AuditPlugin
The interface of audit plugin
2. AuditEvent
An AuditEvent contains all information about an audit event, such as a query, or a connection.
3. AuditEventProcessor
Audit event processor receive all audit events and deliver them to all installed audit plugins.
This CL implements two audit module plugins:
1. The builtin plugin `AuditLogBuilder`, which act same as the previous logic, to save the
audit log to the `fe.audit.log`
2. An optional plugin `AuditLoader`, which will periodically inserts the audit log into a Doris table
specified by the user. In this way, users can conveniently use SQL to query and analyze this
audit log table.
Some documents are added:
1. HELP docs of install/uninstall/show plugin.
2. Rename the `README.md` in `fe_plugins/` dir to `plugin-development-manual.md` and move
it to the `docs/` dir
3. `audit-plugin.md` to introduce the usage of `AuditLoader` plugin.
ISSUE： #3226
