Pos validator uptime

[arturrez]

Why this should be merged

adds PoS proof of uptime support for removeValitor

How this works

if uptime is not provided, it's calculated from evm getCurrentValdators api.
Signature aggregator is used to sign proof of uptime msg which is submitted to ValidatorManager smart contract

How this was tested

./bin/avalanche node local start  --num-nodes 7 --etna-devnet local7
./bin/avalanche blockchain create pos7 --proof-of-stake  --force  --evm --reward-basis-points 10000000 // make sure that validator gets reward even after short staking period
./bin/avalanche blockchain deploy pos7 --cluster local7 --bootstrap-endpoints http://127.0.0.1:9650/,http://127.0.0.1:9652/,http://127.0.0.1:9654/,http://127.0.0.1:9656/,http://127.0.0.1:9658/  --convert-only
./bin/avalanche node local track local7 pos7
./bin/avalanche contract initValidatorManager pos7  --cluster local7
./bin/avalanche blockchain addValidator pos7  --cluster local7 --node-endpoint http://127.0.0.1:9660
sleep 120s
./bin/avalanche blockchain removeValidator pos7  --cluster local7 --node-endpoint http://127.0.0.1:9660

How is this documented