These changes are the implementation of concepts outlined in
designs/extensible-cli-and-scaffolding-plugins-phase-1.md

* cmd/: remove all but 'edit' and 'update' subcommands in favor
of plugins that implement removed commands

* internal/cmdutil: RunOptions configure Run() to execute a command
in a generic manner

* pkg/cli: CLI interface and cobra CLI constructors. Most commands
from cmd/ were move here and modified to initialize plugins

* pkg/plugin: Plugin and PluginGetter interfaces for v1 and v2
scaffolds. These are kubebuilider's base Go plugins consumed by
pkg/cli.CLI

pkg/plugin: validation for plugin version strings

pkg/internal/validation: project-wide validation logic; move
pkg/model/resource/validation.go functions here

internal type

pkg/plugin: InjectConfig passes a Config object to a plugin that
the plugin can modify instead of having the plugin load/save the
plugin itself

pkg/cli: manage initialization, loading, and saving of a Config
object, and inject the Config object into plugins

internal/cmdutil: remove LoadConfig and Config object parameters
from RunOptions interface

cmd: rewrite edit/update to respect new command runner interface

should run for a subcommand. This option is global. Refactoring of
getBaseFlags -> parseBaseFlags allows multiple global flags to be
parsed for a cli struct. plugin filtering considers short names,
ex. --plugins="go" rather than --plugins="go.kubebuilder.io/v2.0.0".
WithDefaultPlugins sets the default plugins a CLi should use in case
--plugins or the config 'layout' are not set

pkg/model/config: Config support the 'layout' key which indicates the
plugin that scaffolded a project, by plugin key

pkg/plugin: SplitKey, KeyFor, Key, GetShortName are utility functions
for plugin keys

* pkg/{cli,plugin}: add plugin name validation

* pkg/plugin/{v1,v2}: set layout key in config

 Please enter the commit message for your changes. Lines starting

'plugins' key, with each plugin's config keyed by its plugin key,
and an encoder and decoder for plugin configuration objects. Add
marshal/unmarshal functions for a Config

internal/config: use Config marshalling/unmarshalling to read/write
a config, and add tests

… a version

bump. This new version will be '3-alpha', which will eventually be bumped to
'3' once the below config changes have stabilized.

*: add tests and checks for v3 where appropriate

testdata: add v3 test data

the correct command name

pkg/cli: use layout or cliPluginKeys in error messages if no plugin
for a command is found

to be used for scaffolding at a time, and a config's 'layout' value
should be used for other commands. Also change the implementation of
resolvePluginsByKey to only match one key, and add tests

all encode/decode operations on a Config methods

… "3-alpha",

and update all references

pkg/cli: generalize layout key check for future v3 project version types