Add show plugins and triggers

[pauldix]

Add support to the CLI and API to show plugins and triggers. Currently you can only see them through the system tables.

[hiltontj]

Wondering if this can be closed now. The influxdb3 show system command can be used to display configured triggers per database, e.g.,

❯ influxdb3 show system --database foo table processing_engine_triggers
+--------------+--------------------------------------+------------------------+----------+
| trigger_name | plugin_filename                      | trigger_specification  | disabled |
+--------------+--------------------------------------+------------------------+----------+
| trig         | gh:examples/wal_plugin/wal_plugin.py | "all_tables_wal_write" | false    |
+--------------+--------------------------------------+------------------------+----------+

[pauldix]

yeah, closing this for now