Enhance ValidatedSoftware associations

[mzbroch]

Existing Functionality

The plugin allows for limited flexibility when working with ValidatedSoftware model instances.

The user is limited to create only one of the following per the single ValidatedSoftware instance:

• one association to Device
• one association to DeviceType
• one association to InventoryItem

Proposed Functionality

While working with networks of hundreds or thousands of objects, it has been identified current way of managing the ValidatedSoftware is cumbersome.

Most likely, a given software release will be applicable to multiple Device(s) or multiple DeviceType(s) or multiple InventoryType(s) or Groups having the same lifecycle (valid from, valid until etc.).

Proposed functionality assumes following:
ValidatedSoftware instance pointing to a mix of Device, DeviceTypes and CustomGroups (nautobot/nautobot#896).

Use Case

As a Network Engineer, I want to have limited number of ValidatedSoftware to ease maintenance.

As a Network Engineer, I want to assign a ValidatedSoftware instance (one) for different and multiple types of objects (mix of Device, DeviceTypes and objects groups.)

[progala]

Raised #32 which implements multiple object assignments for ValidatedSoftware.

[dgarros]

Fixed in #32