eth, les, params: log chain config a bit saner (#24904)

Previously on Geth startup we just logged the chain config is a semi-json-y format. Whilst that worked while we had a handful of hard-forks defined, currently it's kind of unwieldy. 

This PR converts that original data dump and converts it into a user friendly - alas multiline - log output.

core/forkid/forkid_test.go

@@ -31,7 +31,7 @@ import (
 // the correct fork ID.
 func TestCreation(t *testing.T) {
 	mergeConfig := *params.MainnetChainConfig
-	mergeConfig.MergeForkBlock = big.NewInt(15000000)
+	mergeConfig.MergeNetsplitBlock = big.NewInt(15000000)
 	type testcase struct {
 		head uint64
 		want ID