GC: Add Service to graph/betasdk package (#2298)

## Description
Creates Beta Service for betasdk package. Abstraction loosely complies with the methods found in `graph.Servicer()`. 
Will aid when Sharepoint functionality is supported in v1.0 and `betasdk` package is removed. 
<!-- Insert PR description-->

## Does this PR need a docs update or release note?
- [x] ⛔ No 

## Type of change

<!--- Please check the type of change your PR introduces: --->
- [x] 🌻 Feature

## Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
- related to * #2174<issue>

## Test Plan

<!-- How will this be tested prior to merging.-->
- [x] 💪 Manual

src/internal/connector/discovery/api/beta_service.go

@@ -0,0 +1,43 @@
+package api
+
+import (
+	"github.com/alcionai/corso/src/internal/connector/graph/betasdk"
+	absser "github.com/microsoft/kiota-abstractions-go/serialization"
+	msgraphsdk "github.com/microsoftgraph/msgraph-sdk-go"
+	"github.com/pkg/errors"
+)
+
+// Service wraps BetaClient's functionality.
+// Abstraction created to comply loosely with graph.Servicer
+// methods for ease of switching between v1.0 and beta connnectors
+type Service struct {
+	client *betasdk.BetaClient
+}
+
+func (s Service) Client() *betasdk.BetaClient {
+	return s.client
+}
+
+func NewBetaService(adpt *msgraphsdk.GraphRequestAdapter) *Service {
+	return &Service{
+		client: betasdk.NewBetaClient(adpt),
+	}
+}
+
+// Seraialize writes an M365 parsable object into a byte array using the built-in
+// application/json writer within the adapter.
+func (s Service) Serialize(object absser.Parsable) ([]byte, error) {
+	writer, err := s.client.Adapter().
+		GetSerializationWriterFactory().
+		GetSerializationWriter("application/json")
+	if err != nil || writer == nil {
+		return nil, errors.Wrap(err, "creating json serialization writer")
+	}
+
+	err = writer.WriteObjectValue("", object)
+	if err != nil {
+		return nil, errors.Wrap(err, "writeObjecValue serialization")
+	}
+
+	return writer.GetSerializedContent()
+}

src/internal/connector/discovery/api/beta_service_test.go

@@ -0,0 +1,49 @@
+package api
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/stretchr/testify/suite"
+
+	"github.com/alcionai/corso/src/internal/connector/graph"
+	"github.com/alcionai/corso/src/internal/connector/graph/betasdk/models"
+	"github.com/alcionai/corso/src/internal/tester"
+)
+
+type BetaUnitSuite struct {
+	suite.Suite
+}
+
+func TestBetaUnitSuite(t *testing.T) {
+	suite.Run(t, new(BetaUnitSuite))
+}
+
+func (suite *BetaUnitSuite) TestBetaService_Adapter() {
+	t := suite.T()
+	a := tester.NewM365Account(t)
+	m365, err := a.M365Config()
+	require.NoError(t, err)
+
+	adpt, err := graph.CreateAdapter(
+		m365.AzureTenantID,
+		m365.AzureClientID,
+		m365.AzureClientSecret,
+	)
+	require.NoError(t, err)
+
+	service := NewBetaService(adpt)
+	require.NotNil(t, service)
+
+	testPage := models.NewSitePage()
+	name := "testFile"
+	desc := "working with parsing"
+
+	testPage.SetName(&name)
+	testPage.SetDescription(&desc)
+
+	byteArray, err := service.Serialize(testPage)
+	assert.NotEmpty(t, byteArray)
+	assert.NoError(t, err)
+}

src/internal/connector/graph/betasdk/beta_client.go

@@ -84,3 +84,8 @@ func (m *BetaClient) SitesById(id string) *i1a3c1a5501c5e41b7fd169f2d4c768dce9b0
 	}
 	return i1a3c1a5501c5e41b7fd169f2d4c768dce9b096ac28fb5431bf02afcc57295411.NewSiteItemRequestBuilderInternal(urlTplParams, m.requestAdapter)
 }
+
+// Adapter() helper method to export Adapter for iterating
+func (m *BetaClient) Adapter() *msgraphsdk.GraphRequestAdapter {
+	return m.requestAdapter
+}