prysmctl support generating non-phase0 genesis.ssz (#11677)

* support generating non-phase0 genesis.ssz

* make default (Value) work for EnumValue + lint

* remove messy punctuation

* Ran gazelle for @kasey

* Fix deps viz

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>
Co-authored-by: prestonvanloon <preston@prysmaticlabs.com>

cmd/flags/BUILD.bazel

@@ -0,0 +1,9 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["enum.go"],
+    importpath = "github.com/prysmaticlabs/prysm/v3/cmd/flags",
+    visibility = ["//visibility:public"],
+    deps = ["@com_github_urfave_cli_v2//:go_default_library"],
+)

cmd/flags/enum.go

@@ -0,0 +1,47 @@
+package flags
+
+// via https://github.com/urfave/cli/issues/602
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/urfave/cli/v2"
+)
+
+// EnumValue allows the cli to present a fixed set of string values.
+type EnumValue struct {
+	Name        string
+	Usage       string
+	Destination *string
+	Enum        []string
+	Value       string
+}
+
+func (e *EnumValue) Set(value string) error {
+	for _, enum := range e.Enum {
+		if enum == value {
+			*e.Destination = value
+			return nil
+		}
+	}
+
+	return fmt.Errorf("allowed values are %s", strings.Join(e.Enum, ", "))
+}
+
+func (e *EnumValue) String() string {
+	if e.Destination == nil {
+		return e.Value
+	}
+	if *e.Destination == "" {
+		return e.Value
+	}
+	return *e.Destination
+}
+
+// Wraps the EnumValue in a GenericFlag value so that it satisfies the cli.Flag interface.
+func (e EnumValue) GenericFlag() *cli.GenericFlag {
+	*e.Destination = e.Value
+	var i cli.Generic = &e
+	return &cli.GenericFlag{Name: e.Name, Usage: e.Usage, Destination: &i, Value: i}
+}