add pausable uptime manager

[ceyonur]

Why this should be merged

Adds pausable uptime manager interface for uptime tracking

How this works

Pausable uptime manager extends the avalanchego uptime manager by introducing callback listeners for validators state (under plugin/evm/validators). The idea is to pause a node's uptime and then can continue whenever it's resumed. It also modifies Connect, Disconnect, StartTracking` accordingly.

How this was tested

Added tests

How is this documented

Comments in code