Add Version func to otel/sdk (#3949)

* Add Version func to otel/sdk

* Update sdk/resource to use sdk version

* Remove unused UserAgent from sdk/internal

* Add changes to changelog

* Update CHANGELOG.md

Co-authored-by: Robert Pająk <pellared@hotmail.com>

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>

sdk/version_test.go

@@ -0,0 +1,34 @@
+// 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 sdk_test
+
+import (
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel"
+)
+
+// regex taken from https://github.com/Masterminds/semver/tree/v3.1.1
+var versionRegex = regexp.MustCompile(`^v?([0-9]+)(\.[0-9]+)?(\.[0-9]+)?` +
+	`(-([0-9A-Za-z\-]+(\.[0-9A-Za-z\-]+)*))?` +
+	`(\+([0-9A-Za-z\-]+(\.[0-9A-Za-z\-]+)*))?$`)
+
+func TestVersionSemver(t *testing.T) {
+	v := otel.Version()
+	assert.NotNil(t, versionRegex.FindStringSubmatch(v), "version is not semver: %s", v)
+}