Disambiguates some units. (#19875)

* Disambiguates some units.

* Updates DB attribute.

* Updates some more error-prone units.

* Updates some tests with legible constants.

* Updates query for MySQL case sensitivity.

* Fixes more casing issues.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/channel_test.go

@@ -1169,8 +1169,8 @@ func TestGetAllChannels(t *testing.T) {
 	policyChannel := (sysManagerChannels)[0]
 	policy, err := th.App.Srv().Store.RetentionPolicy().Save(&model.RetentionPolicyWithTeamAndChannelIDs{
 		RetentionPolicy: model.RetentionPolicy{
-			DisplayName:  "Policy 1",
-			PostDuration: model.NewInt64(30),
+			DisplayName:      "Policy 1",
+			PostDurationDays: model.NewInt64(30),
 		},
 		ChannelIDs: []string{policyChannel.Id},
 	})
@@ -1621,8 +1621,8 @@ func TestSearchAllChannels(t *testing.T) {
 	policyChannel := sysManagerChannels[0]
 	policy, savePolicyErr := th.App.Srv().Store.RetentionPolicy().Save(&model.RetentionPolicyWithTeamAndChannelIDs{
 		RetentionPolicy: model.RetentionPolicy{
-			DisplayName:  "Policy 1",
-			PostDuration: model.NewInt64(30),
+			DisplayName:      "Policy 1",
+			PostDurationDays: model.NewInt64(30),
 		},
 		ChannelIDs: []string{policyChannel.Id},
 	})