OS and Process resource detectors (#1788)

* WIP: OS and Process resource detectors

* Completed documentation headers

* Added empty test files for OS and Process resource functions

* Split long line

* Added resource.WithOS function test

* Added resource.WithProcess* functions tests

* Renamed osDetector and WithOS function to better reflect they only add the os.type attribute

* Updated changelog

* WIP: possible use of wrappers for getting attribute values

* Refined implementation of wrapper functions providing os/runtime/user information

* Added PR number to new changelog entries

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Fix wrong function name in documentation header

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Fixed wording in WithProcessOwner documentation header

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Updated osTypeDetector

* Replaced ToUpper with ToLower to match the current convention.
* Used runtimeOS provider to get the OS name.

* Adapted WithOSType test to mock runtime providers

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

sdk/resource/os_test.go

@@ -0,0 +1,51 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package resource_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/otel/sdk/resource"
+)
+
+func mockRuntimeProviders() {
+	resource.SetRuntimeProviders(
+		fakeRuntimeNameProvider,
+		fakeRuntimeVersionProvider,
+		func() string { return "LINUX" },
+		fakeRuntimeArchProvider,
+	)
+}
+
+func TestWithOSType(t *testing.T) {
+	mockRuntimeProviders()
+
+	ctx := context.Background()
+
+	res, err := resource.New(ctx,
+		resource.WithoutBuiltin(),
+		resource.WithOSType(),
+	)
+
+	require.NoError(t, err)
+	require.EqualValues(t, map[string]string{
+		"os.type": "linux",
+	}, toMap(res))
+
+	restoreProcessAttributesProviders()
+}