m.room.retention: add the expire_on_clients option

I doubt anything implements it, but hopefully Synapse implementation contains it

matrix/retention/1h.json

@@ -1,4 +1,5 @@
 {
       "min_lifetime": 3600000,
-      "max_lifetime": 3600000
+      "max_lifetime": 3600000,
+      "expire_on_clients": true
 }

matrix/retention/24h.json

@@ -1,4 +1,5 @@
 {
       "min_lifetime": 86400000,
-      "max_lifetime": 86400000
+      "max_lifetime": 86400000,
+      "expire_on_clients": true
 }

matrix/retention/31days.json

@@ -1,4 +1,5 @@
 {
       "min_lifetime": 86400000,
-      "max_lifetime": 2678400000
+      "max_lifetime": 2678400000,
+      "expire_on_clients": true
 }

matrix/retention/README.md

@@ -6,6 +6,7 @@ Read that, it explains what is actually done etc.
 
 ## Notes
 
+* Not part of spec. https://github.com/matrix-org/matrix-spec-proposals/pull/1763
 * Matrix uses milliseconds, keep that in mind!
 * Everything requires every server involved to have rention support enabled,
   otherwise the messages go nowhere and are fetchable upon request.

matrix/retention/week.json

@@ -1,4 +1,5 @@
 {
       "min_lifetime": 86400000,
-      "max_lifetime": 604800000
+      "max_lifetime": 604800000,
+      "expire_on_clients": true
 }