Add Why and Common Use Cases to Deploy Token and Deploy Key documentation
Problem to solve
Current deploy token and deploy key documentation doesn't provide the Why and common usage patterns for the feature.
Discussed in this Slack thread - https://gitlab.slack.com/archives/C0AR2KW4B/p1593181516300700
Today the Deploy Key and Deploy Token (Project and Group) documentation emphasize what you can do with the tokens and keys but not why you would want to do that and common use cases.
Add some of the common use cases described in the Slack thread to our user documentation around Deploy Keys and Deploy Tokens.