Fix GCP redirect

Closes #41867

See merge request gitlab-org/gitlab-ce!16355

(cherry picked from commit 59adc07f)

b44583e9 Extract GCP billing check as method
cf6258af Fix billing checking
0cdd56e6 Fix link to billing
e52bae3b Fix CheckGcpProjectBillingService spec
b8b2f5ff Fix CheckGcpProjectBillingWorker spec
8ba3e473 Fix GCP Controller spec
1f0a4fe6 Add missing user agent header to GCP client
6ef28ace Add API requirements to docs
0b294fc2 Use new tab for link in flash
cf95756a Refactor GCP redirect test suite
e6012d3e Change failed GCP billing check wording
35598274 Fix breadcumb of clusters show page
cf842986 Update links for GCP instructions