add handlers for channels (#4050)

<!-- PR description-->

add Handlers interface for Channels. 

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

#### Type of change

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

#### Issue(s)

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

#### Test Plan

<!-- How will this be tested prior to merging.-->

src/internal/m365/collection/groups/handler.go

@@ -0,0 +1,18 @@
+package groups
+
+import (
+	"context"
+
+	"github.com/microsoft/kiota-abstractions-go/serialization"
+	"github.com/microsoftgraph/msgraph-sdk-go/models"
+
+	"github.com/alcionai/corso/src/pkg/services/m365/api"
+)
+
+type BackupMessagesHandler interface {
+	GetMessageByID(ctx context.Context, teamID, channelID, itemID string) (models.ChatMessageable, error)
+	NewMessagePager(teamID, channelID string) api.MessageItemDeltaEnumerator
+	GetChannelByID(ctx context.Context, teamID, channelID string) (models.Channelable, error)
+	NewChannelPager(teamID, channelID string) api.ChannelItemDeltaEnumerator
+	GetReplyByID(ctx context.Context, teamID, channelID, messageID string) (serialization.Parsable, error)
+}

src/pkg/services/m365/api/channels.go

@@ -0,0 +1 @@
+package api

src/pkg/services/m365/api/channels_pager.go

@@ -0,0 +1,39 @@
+package api
+
+import (
+	"context"
+)
+
+// ---------------------------------------------------------------------------
+// item pager
+// ---------------------------------------------------------------------------
+
+type MessageItemDeltaEnumerator interface {
+	GetPage(context.Context) (DeltaPageLinker, error)
+}
+
+// TODO: implement
+// var _ MessageItemDeltaEnumerator = &messagePageCtrl{}
+
+// type messagePageCtrl struct {
+// 	gs      graph.Servicer
+// 	builder *teams.ItemChannelsItemMessagesRequestBuilder
+// 	options *teams.ItemChannelsItemMessagesRequestBuilderGetRequestConfiguration
+// }
+
+// ---------------------------------------------------------------------------
+// channel pager
+// ---------------------------------------------------------------------------
+
+type ChannelItemDeltaEnumerator interface {
+	GetPage(context.Context) (DeltaPageLinker, error)
+}
+
+// TODO: implement
+// var _ ChannelsItemDeltaEnumerator = &channelsPageCtrl{}
+
+// type channelsPageCtrl struct {
+// 	gs      graph.Servicer
+// 	builder *teams.ItemChannelsChannelItemRequestBuilder
+// 	options *teams.ItemChannelsChannelItemRequestBuilderGetRequestConfiguration
+// }