cmd/geth, cmd/utils: geth attach with custom headers (#25829)

This PR makes it possible to set custom headers, in particular for two scenarios: 

- geth attach
- geth commands which can use --remotedb, e..g geth db inspect

The ability to use custom headers is typically useful for connecting to cloud-apis, e.g. providing an infura- or alchemy key, or for that matter access-keys for environments behind cloudflare.  

Co-authored-by: Felix Lange <fjl@twurst.com>

ethdb/remotedb/remotedb.go

@@ -22,9 +22,6 @@
 package remotedb
 
 import (
-	"errors"
-	"strings"
-
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -150,24 +147,8 @@ func (db *Database) Close() error {
 	return nil
 }
 
-func dialRPC(endpoint string) (*rpc.Client, error) {
-	if endpoint == "" {
-		return nil, errors.New("endpoint must be specified")
-	}
-	if strings.HasPrefix(endpoint, "rpc:") || strings.HasPrefix(endpoint, "ipc:") {
-		// Backwards compatibility with geth < 1.5 which required
-		// these prefixes.
-		endpoint = endpoint[4:]
-	}
-	return rpc.Dial(endpoint)
-}
-
-func New(endpoint string) (ethdb.Database, error) {
-	client, err := dialRPC(endpoint)
-	if err != nil {
-		return nil, err
-	}
+func New(client *rpc.Client) ethdb.Database {
 	return &Database{
 		remote: client,
-	}, nil
+	}
 }