Update users: add server pick-list

[TC1977]

Description

When updating users, you no longer have to type out the entire IP address or domain name (or 'localhost') of the Algo server that you deployed and want to update. This might also be helpful if you've deployed multiple Algo servers.

Motivation and Context

Closes #1438. Typing a whole IP address is hard. Cutting-and-pasting is also hard. Typing a number is easy.

How Has This Been Tested?

Numerous runs of ansible-playbook users.yml.

Types of changes

• [] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• [] My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• [] I have added tests to cover my changes.
• [] All new and existing tests passed.

[jackivanov]

Should we add additional info to the list, like cloud, region and server name? Something like this:

Select the server to update user list below:
  1. DigitalOcean   fra1        test-server-01    206.189.19.82
  2. EC2            eu-west-1   prod-server-01    18.203.231.98

So it could be more clearly

[TC1977]

I don't need it myself, but I think it would be really useful for people running multiple servers.

[jackivanov]

let's leave it as is for now