perf(command): user grant pre-condition check using the search table (#8230)

# Which Problems Are Solved

Imporve the performance of user grant addition, especially for import.

# How the Problems Are Solved

Use the search table to query for the project grant state. 
This could easily be done by making the search used in
`checkProjectGrantPreCondition` reusable.

# Additional Changes

Chanded event declerations to `const` in the
`internal/repository/project` package.

# Additional Context

- Performance improvements for import are evaluated and acted upon
internally at the moment

---------

Co-authored-by: adlerhurst <silvan.reusser@gmail.com>
Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/repository/project/role.go

@@ -8,7 +8,7 @@ import (
 	"github.com/zitadel/zitadel/internal/zerrors"
 )
 
-var (
+const (
 	UniqueRoleType      = "project_role"
 	roleEventTypePrefix = projectEventTypePrefix + "role."
 	RoleAddedType       = roleEventTypePrefix + "added"