Validation for set cmd attributes (profile, url, etc)

[sureshanaparti]

There should be some validation (atleast null/empty checks, invalid urls) for the values set through the set cmd in cli.

Checked (in cmk 6.3.0 / 6.4.0 RC1) with some empty values for profile and url, these are updated without any errors and the cmds after that doesn't work.

(cmk) 🐱 > set profile
Loaded in-built API cache. Failed to read API cache, please run 'sync'.
Loaded server profile: 
Url:         
Username:    
Domain:      
API Key:     
Total APIs:  754

(cmk) 🐱 > list hosts details=min
Please provide either apikey/secretkey or username/password to make an API call
🙈 Error: failed to authenticate to make API call

(cmk) 🐱 > set url
(cmk) 🐱 > list hosts details=min
🙈 Error: Get "?apiKey=LIN6rqXuaJwMPfGYFh13qDwYz5VNNz1J2J6qIOWcd3oLQOq0WtD4CwRundBL6rzXToa3lQOC_vKjI3nkHtiD8Q&command=listHosts&details=min&response=json&signature=kwv%2FgM82BQpTrmw9byW97agy7lQ%3D": unsupported protocol scheme ""