feat: extend premium license for aigovernance (#21499)

Closes [#1227](https://github.com/coder/internal/issues/1227)

Added support for license addons, starting with AI Governance, to enable
dynamic feature grouping without requiring license reissuance.

### What changed?

- Introduced a new `Addon` type to represent groupings of features that
can be added to licenses
- Created the first addon `AddonAIGovernance` which includes AI Bridge
and Boundary features
- Added validation for addon dependencies to ensure required features
are present
- Added new features: `FeatureBoundary` and
`FeatureAIGovernanceUserLimit`
- Updated license entitlement logic to handle addons and their features
- Added helper methods to check if features belong to addons
- Updated tests to verify addon functionality

### Why make this change?

This change introduces a more flexible licensing model that allows
features to be grouped into addons that can be added to licenses without
requiring reissuance when new features are added to an addon. This is
particularly useful for specialized feature sets like AI Governance,
where related features can be bundled together and sold as a separate
SKU. The addon approach allows for better organization of features and
more granular control over entitlements.

codersdk/deployment_test.go

@@ -623,7 +623,8 @@ func TestPremiumSuperSet(t *testing.T) {
 	// Premium ⊃ Enterprise
 	require.Subset(t, premium.Features(), enterprise.Features(), "premium should be a superset of enterprise. If this fails, update the premium feature set to include all enterprise features.")
 
-	// Premium = All Features EXCEPT usage limit features
+	// Premium = All Features EXCEPT limit-based features.
+	// TODO: In future release, also exclude addon features (f.IsAddonFeature()).
 	expectedPremiumFeatures := []codersdk.FeatureName{}
 	for _, feature := range codersdk.FeatureNames {
 		if feature.UsesLimit() {