Update the Vault documentation for the OIDC authentication change from Google to Okta
Also update the Hashicorp Vault documentation URLs to the new ones.
Part of https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16926
Also update the Hashicorp Vault documentation URLs to the new ones.
Part of https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16926