Make switching accounts easy
It will need https://gitlab.com/gitlab-org/gitlab-ce/issues/30484 to be finished first
#### Problem
There is no easy way of switching profiles within gitlab.
#### Proposal
Create a similar functionality as how google does this.

- Add account option
- Accounts are displayed under each other, when clicked on switch account
#### Value
Easier switching of account, based on cookie (if i am correct)
#### Related issues
https://gitlab.com/gitlab-org/gitlab-ce/issues/30484
#### CC/Call to actions
@alfredo1 @tauriedavis @victorwu @JobV (how hard will this be, what priority can we give this?)
epic