Fix provider name in lookup objects

[FlorianBracq]

With the current implementation, the ChainMap of providers for a lookup will use the "settings.Provider" value, which means that if you define 2 providers with the same type but different names (for instance when using 2 instances of the same provider), only one provider would be available in lookup._all_providers

This can be tested with:

ContextProviders:
  Instance1:
    Args:
      Instance: instance1
      ApiID: valueA1
      AuthKey: valueA2
    Primary: True
    Provider: ServiceNow
  Instance2:
    Args:
      Instance: instance2
      ApiID: valueB1
      AuthKey: valueB2
    Primary: True
    Provider: ServiceNow

the chainmap is:
ChainMap({}, {'ServiceNow': <msticpy.context.contextproviders.servicenow.ServiceNow object at 0x7f737c4156d0>})

while it should be:

ChainMap({}, {'Instance1': <msticpy.context.contextproviders.servicenow.ServiceNow object at 0x7f737c4156d0>, 'Instance2': <msticpy.context.contextproviders.servicenow.ServiceNow object at 0x7f737c4156d1>}

[ianhelle]

This is awesome Florian! I've known that this was a problem for ages and always wanted to get to fix it.