add VPN setup instructions to RM template

This MR adds VPN setup step to access request template for release managers.

Related issues:

• https://gitlab.com/gitlab-com/infrastructure/issues/2207
• https://gitlab.com/gitlab-org/release-tools/issues/87

And vim auto cleaned two whitespaces at EOLs, @jamedjo please let me know if I need to drop those from MR.