Adding CRIME Vulnerability to Security doc

Added an additional page to the security section that goes over current status and fixes for the TLS Protocol CRIME Vulnerability. Also added its respective link at the security README.

Any suggestions appreciated @JobV @sytses

@jacobvosmaer knows more than me, maybe he can give his insights.

Please see what I wrote in https://gitlab.com/gitlab-org/gitlab-ce/issues/4088#note_2955917

@jacobvosmaer As far as I understand this vulnerability only checks if SPDY is enabled and if it's advertised with a version lower than 4. Nessus doesn't executive an attack. This of course implies that it could be vulnerable not that it is. This is what I understand from their report though.

This MR request should wait until the current issue at dev is resolved. Will follow up there.

Added 128 commits:

• 75553b12...27859f7e - 124 commits from branch master
• e967748a - Adding CRIME vulnerability to security docs
• ad975c72 - Adding CRIME link to security README [ci skip]
• 8403694f - Changing docs to How we manage CRIME
• bc7a12f2 - Changing title from index and fixing MC

Added 5 commits:

• bc7a12f2...4b4cbf0c - 4 commits from branch master
• a3de4665 - Adding how we manage CRIME vulnerability to security docs [ci skip]

Reassigned to @axil

mentioned in issue #4088 (closed)

Thanks @balameb I'll review it later today or tomorrow morning.

Milestone changed to 8.3

Added 220 commits:

• a3de4665...ed777c7b - 218 commits from branch master
• 05f8c585 - Merge branch 'master' into adding_crime_security
• e081edc1 - Clean up CRIME security doc [ci skip]

Status changed to merged

mentioned in commit 9dc1a53b

mentioned in merge request !14289 (merged)

changed the description

added typemaintenance label