Change the admin password for perf environments

Building on @nwestbury's work in https://gitlab.com/gitlab-org/quality/performance-environment-builder/-/merge_requests/62 to make the GitLab admin password configurable via an encrypted file this MR changes the (initial) password for the performance test environments.

The new password won't take effect until we change it manually on each env as the setting is only for when environments are initially built.