[MS01] Move NetworkTemplate cloud backup functions to NetworkPolicy

Since NetworkTemplate will be moved into the mainline module.
It is necessary to remove hidden BackupUtil usage from
NetworkTemplate. Also, it is also a hazard to maintain
compatibility for byte buffer interfaces.

Thus, move out these cloud backup functions to NetworkPolicy
to address these concerns.

Test: atest NetworkPolicyTest NetworkPolicyManagerServiceTest
Bug: 204830222
Change-Id: I3ec55f7e419ea13db535acff2457d8e7aaebdce8