Improve Policy support

[mzbroch]

High Level Overview:
As of today, the policy support implemented in the plugin provides limited user experience with small flexibility. In the technical solution, we use string fields for import and export policies in at least PeerGroup or PeerEndpoint objects (not limited to). Currently implemented solution might require improvements, as we can move to more advanced models for the better user experience.

This issue should track the work needed to improve overall policy related user experience.

Some of low level ideas are:

• object based policies
• policy chain support
• Nautobot Policy integration - plugin, bgp
• • editable policies