HTTP validator API: health endpoints (#13149)

* updating health endpoints

* updating tests

* updating tests

* moving where the header is written and adding allow origin header

* removing header

* Update validator/rpc/handlers_health.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/rpc/handlers_health.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/rpc/handlers_health.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* radek's comments

* Update handlers_health.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* adding the correct errors to handle error

---------

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

io/logs/mock/BUILD.bazel

@@ -0,0 +1,9 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["mock_stream.go"],
+    importpath = "github.com/prysmaticlabs/prysm/v4/io/logs/mock",
+    visibility = ["//visibility:public"],
+    deps = ["//async/event:go_default_library"],
+)

io/logs/mock/mock_stream.go

@@ -0,0 +1,27 @@
+package mock
+
+import "github.com/prysmaticlabs/prysm/v4/async/event"
+
+type MockStreamer struct {
+	logs [][]byte
+	feed *event.Feed
+}
+
+// NewMockStreamer creates a new instance of MockStreamer.
+// It's useful to set up the default state for the mock, like initializing the feed.
+func NewMockStreamer(logs [][]byte) *MockStreamer {
+	return &MockStreamer{
+		logs: logs,
+		feed: new(event.Feed),
+	}
+}
+
+// GetLastFewLogs returns the predefined logs.
+func (m *MockStreamer) GetLastFewLogs() [][]byte {
+	return m.logs
+}
+
+// LogsFeed returns the predefined event feed.
+func (m *MockStreamer) LogsFeed() *event.Feed {
+	return m.feed
+}