Improve validation of CRC Binary and Pull Secret File in CRC Server Wizard and Editor

I can image improved validation of Pull secret file that is available in CRC Server wizard and Server Editor.

Missing validation of CRC Binary:

• Please select a valid CRC Binary, which would check that file is really a crc binary - we used similar validation for minishift where (I f I recall it right) we checked in process the output from `minishift version` or `minishift status` command. Something similar I can imagine to be used for crc. Since `crc status` could return different outputs, version seems to be better option. I would agree to postpone this validation once the crc is GA. then please ignore this and create new jira issue. Thanks!

I can imagine all of those validation in action for pull secret path input:

• Path does not exist
• Is not a file
• Is not executable (user cannot read the file)
• Is not a valid Pull secret file (probably check for if file's content is a valid json and/or we can probably validate if json's first object is "auths"? This would be nice, but simple json validation seems fine)

I believe that last three points could be validated at once by reading the file's content and creating valid json object, or else showing the error that given path is no valid a secret file. It's up implementation, right?