Move leases away from package subnet

[manuelbuil]

Signed-off-by: Manuel Buil [email protected]

Description

Trying to declutter the subnet package which is big and contains lots of different stuff. In this case, I am trying to move everything around leases into its own package. Summary::

• Create "package lease" which includes the structs: Event, LeaseAttrs, Lease, LeaseWatchResult and LeaseWatcher
• Remove "(l *Lease) Key()" function which was only used in etcd tests. Create it there
• Remove "MarshalJSON()" and "UnmarshalJSON()" functions from EventType because they were never used
• Remove file pkg/subnet/watch.go and move its content into "package lease" or "package subnet" depending on where it makes sense

Todos

• Tests
• Documentation
• Release note

Release Note

None required