Use .json extension for message exports (#4600)

We were previously exporting json but without the proper file extension.

---

#### Does this PR need a docs update or release note?

- [x] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [ ] ⛔ No

#### Type of change

<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* closes https://github.com/alcionai/corso/issues/4581

#### Test Plan

<!-- How will this be tested prior to merging.-->
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased] (beta)
 
+### Changed
+- Change file extension of messages export to json to match the content
+
 ## [v0.15.0] (beta) - 2023-10-31
 
 ### Added

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

@@ -61,10 +61,12 @@ func streamItems(
 				stats.UpdateResourceCount(path.ChannelMessagesCategory)
 				body = data.ReaderWithStats(body, path.ChannelMessagesCategory, stats)
 
+				// messages are exported as json and should be named as such
+				name := item.ID() + ".json"
+
 				ch <- export.Item{
-					ID: item.ID(),
-					// channel message items have no name
-					Name: item.ID(),
+					ID:   item.ID(),
+					Name: name,
 					Body: body,
 				}
 			}

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

@@ -46,7 +46,7 @@ func (suite *ExportUnitSuite) TestStreamItems() {
 					},
 				},
 			},
-			expectName: "zim",
+			expectName: "zim.json",
 			expectErr:  assert.NoError,
 		},
 		{
@@ -71,7 +71,7 @@ func (suite *ExportUnitSuite) TestStreamItems() {
 					clues.New("I miss my cupcake."),
 				},
 			},
-			expectName: "gir",
+			expectName: "gir.json",
 			expectErr:  assert.Error,
 		},
 	}

src/internal/m365/service/groups/export_test.go

@@ -70,7 +70,7 @@ func (suite *ExportUnitSuite) TestExportRestoreCollections_messages() {
 		expectedItems = []export.Item{
 			{
 				ID:   itemID,
-				Name: dii.Groups.ItemName,
+				Name: dii.Groups.ItemName + ".json",
 				// Body: body, not checked
 			},
 		}