Permit the "waitmax" timeout to be adjusted (with a suitable warning about the length of the cache time)

[swampdogmash]

The current "waitmax" commands used in the agent script use a hard coded value. THis may be better implemeneted as a WATO configurable item that allows the user to define a longer time to wait (particularly for slower, older machines, raspberry pies etc - and any machines with MANY outstanding updates)