Update VoIP providers at module update

[Stell0]

Voip Providers are saved into mysql tables and sometime providers are added or removed.
When a provider is added or removed, existing installations should be updated too. But writing update code for every provider changed is onerous and error-prone

Proposed solution

In previous version providers table was dropped and created again at every update. We should do the same.

Additional context

A sample of a pull request for adding a new provider https://github.com/nethesis/ns8-nethvoice/pull/370/files

[Stell0]

Test case: update an older version of nethvoice and check that newer provided are added as expected