UI setting for shellhub-agent keep alive interval

[ltan10]

Just reviving this issue from previous #215

• Need UI setting to show the default KEEPALIVE_INTERVAL and a field to change SHELLHUB_KEEPALIVE_INTERVAL during add device
• Could possible generate environment variable for user to change the default from 30s

[gustavosbarreto]

Thanks for bringing this up! We've created an issue to track this: #5940