Redirected usn updates traffic to separate service

[samhotep]

Done

• Added a redirect for /security/updates/.* that sends traffic for usn updates to a dedicated service
• This PR should first be tested on staging, and only after this has been merged to staging as well
• Declared the security api url as an env variable

QA

• Check that the demo runs
• After merging to staging, test insertions on /security/updates/*
• Test that CVEs and Notices can be accessed on staging.ubuntu.com

Notes

Before merging

• [ ] The U.C Jenkins job has been updated to deploy to prod only as we test - it should be changed back
• [ ] The security api Jenkins job should also be changed back