feat: add custom org ID to AddOrganizationRequest (#9720)

# Which Problems Are Solved

- It is not possible to specify a custom organization ID when creating
an organization. According to
https://github.com/zitadel/zitadel/discussions/9202#discussioncomment-11929464
this is "an inconsistency in the V2 API".

# How the Problems Are Solved

- Adds the `org_id` as an optional parameter to the
`AddOrganizationRequest` in the `v2beta` API.

# Additional Changes

None. 

# Additional Context

- Discussion
[#9202](https://github.com/zitadel/zitadel/discussions/9202)
- I was mostly interested in how much work it'd be to add this field.
Then after completing this, I thought I'd submit this PR. I won't be
angry if you just close this PR with the reasoning "we didn't ask for
it". 😄
- Even though I don't think this is a breaking change, I didn't add this
to the `v2` API yet (don't know what the process for this is TBH). The
changes should be analogous, so if you want me to, just request it.

---------

Co-authored-by: Stefan Benz <46600784+stebenz@users.noreply.github.com>

internal/api/grpc/org/v2beta/integration_test/org_test.go

@@ -79,6 +79,18 @@ func TestServer_AddOrganization(t *testing.T) {
 			},
 			wantErr: true,
 		},
+		{
+			name: "no admin, custom org ID",
+			ctx:  CTX,
+			req: &org.AddOrganizationRequest{
+				Name:  gofakeit.AppName(),
+				OrgId: gu.Ptr("custom-org-ID"),
+			},
+			want: &org.AddOrganizationResponse{
+				OrganizationId: "custom-org-ID",
+				CreatedAdmins:  []*org.AddOrganizationResponse_CreatedAdmin{},
+			},
+		},
 		{
 			name: "admin with init",
 			ctx:  CTX,