MM-56579: Include deactivated users from DM posts (#25985)

There were 2 separate bugs here:
1. We were not including deactivated users while fetching posts from
DM channels.
2. We were not respecting the includeArchivedChannels flag while
fetching DM channels.

We fix both of these issues here.

```release-note
Include posts from deactivated users in DM channel export. Also
respect the --include-archived-channels flag for DM channels.
```

https://mattermost.atlassian.net/browse/MM-56579

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/store/storetest/mocks/PostStore.go

@@ -141,25 +141,25 @@ func (_m *PostStore) Get(ctx context.Context, id string, opts model.GetPostsOpti
 	return r0, r1
 }
 
-// GetDirectPostParentsForExportAfter provides a mock function with given fields: limit, afterID
-func (_m *PostStore) GetDirectPostParentsForExportAfter(limit int, afterID string) ([]*model.DirectPostForExport, error) {
-	ret := _m.Called(limit, afterID)
+// GetDirectPostParentsForExportAfter provides a mock function with given fields: limit, afterID, includeArchivedChannels
+func (_m *PostStore) GetDirectPostParentsForExportAfter(limit int, afterID string, includeArchivedChannels bool) ([]*model.DirectPostForExport, error) {
+	ret := _m.Called(limit, afterID, includeArchivedChannels)
 
 	var r0 []*model.DirectPostForExport
 	var r1 error
-	if rf, ok := ret.Get(0).(func(int, string) ([]*model.DirectPostForExport, error)); ok {
-		return rf(limit, afterID)
+	if rf, ok := ret.Get(0).(func(int, string, bool) ([]*model.DirectPostForExport, error)); ok {
+		return rf(limit, afterID, includeArchivedChannels)
 	}
-	if rf, ok := ret.Get(0).(func(int, string) []*model.DirectPostForExport); ok {
-		r0 = rf(limit, afterID)
+	if rf, ok := ret.Get(0).(func(int, string, bool) []*model.DirectPostForExport); ok {
+		r0 = rf(limit, afterID, includeArchivedChannels)
 	} else {
 		if ret.Get(0) != nil {
 			r0 = ret.Get(0).([]*model.DirectPostForExport)
 		}
 	}
 
-	if rf, ok := ret.Get(1).(func(int, string) error); ok {
-		r1 = rf(limit, afterID)
+	if rf, ok := ret.Get(1).(func(int, string, bool) error); ok {
+		r1 = rf(limit, afterID, includeArchivedChannels)
 	} else {
 		r1 = ret.Error(1)
 	}

server/channels/store/storetest/post_store.go

@@ -4457,7 +4457,7 @@ func testPostStoreGetDirectPostParentsForExportAfter(t *testing.T, rctx request.
 	p1, nErr = ss.Post().Save(p1)
 	require.NoError(t, nErr)
 
-	r1, nErr := ss.Post().GetDirectPostParentsForExportAfter(10000, strings.Repeat("0", 26))
+	r1, nErr := ss.Post().GetDirectPostParentsForExportAfter(10000, strings.Repeat("0", 26), false)
 	assert.NoError(t, nErr)
 
 	assert.Equal(t, p1.Message, r1[0].Message)
@@ -4514,20 +4514,17 @@ func testPostStoreGetDirectPostParentsForExportAfterDeleted(t *testing.T, rctx r
 	p1.UserId = u1.Id
 	p1.Message = NewTestId()
 	p1.CreateAt = 1000
-	p1, nErr = ss.Post().Save(p1)
+	_, nErr = ss.Post().Save(p1)
 	require.NoError(t, nErr)
 
-	o1a := p1.Clone()
-	o1a.DeleteAt = 1
-	o1a.Message = p1.Message + "BBBBBBBBBB"
-	_, nErr = ss.Post().Update(rctx, o1a, p1)
-	require.NoError(t, nErr)
-
-	r1, nErr := ss.Post().GetDirectPostParentsForExportAfter(10000, strings.Repeat("0", 26))
+	r1, nErr := ss.Post().GetDirectPostParentsForExportAfter(10000, strings.Repeat("0", 26), false)
 	assert.NoError(t, nErr)
-
 	assert.Equal(t, 0, len(r1))
 
+	r1, nErr = ss.Post().GetDirectPostParentsForExportAfter(10000, strings.Repeat("0", 26), true)
+	assert.NoError(t, nErr)
+	assert.Equal(t, 1, len(r1))
+
 	// Manually truncate Channels table until testlib can handle cleanups
 	s.GetMasterX().Exec("TRUNCATE Channels")
 }
@@ -4583,7 +4580,7 @@ func testPostStoreGetDirectPostParentsForExportAfterBatched(t *testing.T, rctx r
 	sort.Slice(postIds, func(i, j int) bool { return postIds[i] < postIds[j] })
 
 	// Get all posts
-	r1, err := ss.Post().GetDirectPostParentsForExportAfter(10000, strings.Repeat("0", 26))
+	r1, err := ss.Post().GetDirectPostParentsForExportAfter(10000, strings.Repeat("0", 26), false)
 	assert.NoError(t, err)
 	assert.Equal(t, len(postIds), len(r1))
 	var exportedPostIds []string
@@ -4594,7 +4591,7 @@ func testPostStoreGetDirectPostParentsForExportAfterBatched(t *testing.T, rctx r
 	assert.ElementsMatch(t, postIds, exportedPostIds)
 
 	// Get 100
-	r1, err = ss.Post().GetDirectPostParentsForExportAfter(100, strings.Repeat("0", 26))
+	r1, err = ss.Post().GetDirectPostParentsForExportAfter(100, strings.Repeat("0", 26), false)
 	assert.NoError(t, err)
 	assert.Equal(t, 100, len(r1))
 	exportedPostIds = []string{}