Plugins add command flags

[kquerna]

Description

In order to allow plugins to add flags to commands, we need a new getCommandFlags lifecycle.
Plugins can use this command to add custom flags that they want to listen for. By default
new flags will be added for all commands. The getCommandFlags lifecycle should allow plugins to also limit
which commands should be effected.

As a first custom, we should update @gasket/plugin-metrics to use the new lifecycle to add the record flag
and drop it (from the command plugin).

Package(s): @gasket/plugin-command

AC:

• Ability for plugins to add custom flags to commands
• Ability to limit which commands receive flags
• Update @gasket/plugin-metrics to add record flag