perf(import): do not check for existing grant ID (#8164)

# Which Problems Are Solved

Improve the performance of the `admin/v1/import` API endpoint.
Specifaclly the import of large amount of project grants.

# How the Problems Are Solved

`AddProjectGrantWithID` and `AddProjectGrantMember` methods of
`Commands` used to get the current state of the Writemodel to check if
the current GrantID or the combination of GrantID & UserID wasn't
already used. However, the Added events already have protection against
duplication by the `UniqueConstaint` methods.

The queries become very slow when there is a great amount of project
grants. Because all the events are pushed to the aggregate ID of the
project, we had to obtain all related project events, including events
of grantIDs we do not care about. This O(n) duration for bached import
jobs adding many organization granted to a single project.

This change removes the unnecesary state query to improve performance.

# Additional Changes

- Add integration tests for import

# Additional Context

- reported internally

go.mod

@@ -179,7 +179,7 @@ require (
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/muesli/clusters v0.0.0-20200529215643-2700303c1762 // indirect
 	github.com/muesli/kmeans v0.3.1 // indirect
-	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2
 	github.com/prometheus/client_golang v1.19.1
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.54.0 // indirect