Add Delete Network call to NMAgent client

[debecerra]

Reason for Change:

This change implements the Delete Network API call in the NMAgent client. Adding this method allows for future changes to invoke the Delete Network call on NMAgent after receiving a Delete Network request in DNC.

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• relevant PR labels added

[tamilmani1989]

@debecerra can you please add a label which component PR related to? (cns or cni or something else)

[timraymond]

@tamilmani1989 It's not related to any component. The nmagent package is independent and can be considered in isolation.