Disable Etna by default on local networks

[michaelkaplan13]

Why this should be merged

When running a local network, the Etna changes should not be activated by default until they are more stable (i.e. activated on Fuji). Otherwise, the local network may break when updating to future AvalancheGo versions.

How this works

Self explanatory

How this was tested

Built and ran /build/avalanchego --network-id=12345. Confirmed activation timestamps using

curl --location 'http://localhost:9650/ext/info' \
--header 'Content-Type: application/json' \
--data '{
    "jsonrpc":"2.0",
    "id"     :1,
    "method" :"info.upgrades"
}'

[StephenButtolph]

lgtm... @ceyonur is this a problematic usage of upgrade.Default here?

avalanchego/tests/fixture/tmpnet/genesis.go

Lines 153 to 154 in 75eb89f

	// TODO: remove this after Etna and set only the chainID
	Config: params.GetChainConfig(upgrade.Default, chainID), // upgrade will be again set by VM according to the snow.Context