feat: mempool: Reduce minimum replace fee from 1.25x to 1.1x (#10416)

However, we're leaving the default at 1.25x for backwards compatibility, for now.

Also:

1. Actually use the configured replace fee ratio.
2. Store said ratios as percentages instead of floats. 1.25, or 1+1/(2^2),
can be represented as a float. 1.1, or 1 + 1/(2 * 5), cannot.

fixes #10415

api/docgen/docgen.go

@@ -401,6 +401,10 @@ func init() {
 		FromBlock: pstring("2301220"),
 		Address:   []ethtypes.EthAddress{ethaddr},
 	})
+
+	percent := types.Percent(123)
+	addExample(percent)
+	addExample(&percent)
 }
 
 func GetAPIType(name, pkg string) (i interface{}, t reflect.Type, permStruct []reflect.Type) {