[upnpcontrol] Send periodic keep alive

[digitaldan]

This sends a periodic search packet to the remote upnp device as part of the thing's refresh cycle. This search request acts as a keep alive mechanism for devices that loose registration.
Fixes #16638

[lsiepel]

Besides the single comment, LGTM.

Will wait for @mherwege to look at it before merging. Do you recommend to backport?

[digitaldan]

Thanks, i would suggest backporting this one.

[mherwege]

I am a bit in doubt about this solution. The binding so far refrained from explicit M-SEARCH calls and relied on the upnp service for this. And you state this issue also appears with Sonos. Would it then not be better to solve this in the transport, like here: https://github.com/openhab/openhab-core/blob/1f9ba2b0eea9daf70515cd36b53c3fe1d2f1e54d/bundles/org.openhab.core.io.transport.upnp/src/main/java/org/openhab/core/io/transport/upnp/internal/UpnpIOServiceImpl.java#L434. Maybe @wborn has an opinion on this.
I am still OK to solve it in the binding if the other options don’t work out, but there are 2 underlying layers (upnp transport and service) that in my opinion should be responsible for the stability of the connection.