Add linter checks to GHA & Fix code to pass lints

Add linter checks to GHA & Fix code to pass lints.
The linters added are:
- whitespace: Tool for detection of leading and trailing whitespace
- gosec: Inspects source code for security problems
- gci: Gci control golang package import order and make it always deterministic
- misspell: Finds commonly misspelled English words in comments
- gomnd: An analyzer to detect magic numbers

The file utils/utils.go is excluded from the checks of gomnd, as uses magic numbers through the code

txselector/txselector_test.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/hermeznetwork/hermez-node/db/l2db"
 	"github.com/hermeznetwork/hermez-node/db/statedb"
-
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )