Register VM and snowman metrics after chain creation

[yacovm]

Why this should be merged

Metrics of VM and snowman should be registered only after the objects they are measuring/monitoring have been constructed in the first place.

How this works

Moves metrics registration to after corresponding object creation

How this was tested

CI

[yacovm]

Doesn't work:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x10389bb93]

goroutine 1 [running]:
github.com/ava-labs/avalanchego/snow/networking/sender.New(0xc0003276b0, {0x156d89f10, 0xc0000bd4a0}, {0x156d8d708, 0xc00065cc60}, {0x104e574a8, 0xc0000fb500}, {0x104e55ec0, 0xc0008afbc0}, 0x2, ...)
        /Users/yacov.manevich/avalanchego/snow/networking/sender/sender.go:78 +0x2b3
github.com/ava-labs/avalanchego/chains.(*manager).createSnowmanChain(0xc000653908, 0xc0003276b0, {0xc003182000, 0x432d6c, 0x866000}, {0x104e5b910, 0xc0003ed5c0}, {0x104e5b910, 0xc00177c3c0}, {0x156d8d660, ...}, ...)
        /Users/yacov.manevich/avalanchego/chains/manager.go:1097 +0x3e5
github.com/ava-labs/avalanchego/chains.(*manager).buildChain(0xc000653908, {{0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...}, ...}, ...)
        /Users/yacov.manevich/avalanchego/chains/manager.go:568 +0xcd5
github.com/ava-labs/avalanchego/chains.(*manager).createChain(0xc000653908, {{0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...}, ...})
        /Users/yacov.manevich/avalanchego/chains/manager.go:388 +0x346
github.com/ava-labs/avalanchego/chains.(*manager).StartChainCreator(0xc000653908, {{0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...}, ...})
        /Users/yacov.manevich/avalanchego/chains/manager.go:1490 +0xa5
github.com/ava-labs/avalanchego/node.(*Node).initChains(0xc000005508, {0xc003182000, 0x432d6c, 0x866000})
        /Users/yacov.manevich/avalanchego/node/node.go:928 +0x175
github.com/ava-labs/avalanchego/node.New(0xc00133a008, {0x104e53a58, 0xc0002a6100}, {0x104e5b998, 0xc001488080})
        /Users/yacov.manevich/avalanchego/node/node.go:274 +0x181d
github.com/ava-labs/avalanchego/app.New({{{0x6fc23ac00, 0x6fc23ac00, 0x6fc23ac00, 0x1bf08eb000}, {{0x0, 0x0}, 0x0, 0x1, 0x0, 0x1, ...}, ...}, ...})
        /Users/yacov.manevich/avalanchego/app/app.go:73 +0x485
main.main()
        /Users/yacov.manevich/avalanchego/main/main.go:64 +0x4a5