[FR] Extend connection retry delay or make it settable

[sargonphin]

Is your feature request related to a problem? Please describe.
During good ol' German Internet losses, the IoT adapter will try repeatedly to reconnect with short delays (10 seconds) which is too fast for DSL connection. It takes roughly 2 minutes for Internet to reconnect

Describe the solution you'd like
One of the following would be an adequate solution:

• Increase delay to 30 seconds
• Increment delay after successive failures (first retry is immediate, second retry 5 seconds, third retry is 10, 20, 30, then every minute)
• A settable delay in the adapter options
• A way to detect missing Internet connection and adjusting adapter behavior (log output, connection attempts) depending on the state of the connection, maybe using the ping solution described below

Describe alternatives you've considered
Disabling log output or pausing the adapter altogether to avoid excessive error generation in the logs using the following indicators:

• In the TR-064 adapter connected to the Fritzbox, I tried to find a state that corresponds to Internet connection but didn't find anything reliable
• Using the ping adapter, ping a reliable Internet address (Google DNS 8.8.8.8) every 5 seconds and consider Internet disconnected after 3 failed attempts

[ScumbagSteve]

I was just about to open an issue as well.
This would be a useful improvement. Just yesterday I noticed the adapter was down for me. Turned out I lost my internet connection for a few minutes in the evening and after some retries ioBroker detected a "reboot loop" for the adapter and did not try anymore.

We should cover at least 10-15 minutes of internet downtime before ioBroker detects a reboot loop.