feat: add support for canister properties

spec/index.adoc

@@ -420,7 +420,7 @@ The certified data of the canister with the given id, see <<system-api-certified
 [#state-tree-canister-information]
 === Canister information
 
-Users have the ability to learn about the hash of the canister's module, its current controllers, and metadata in a certified way.
+Users have the ability to learn about the hash of the canister's module, its current controllers, metadata and properties in a certified way.
 
 * `/canister/<canister_id>/module_hash` (blob):
 +
@@ -438,6 +438,15 @@ If the canister has a https://webassembly.github.io/spec/core/binary/modules.htm
 +
 It is recommended for the canister to have a custom section called "icp:public candid:service", which contains the UTF-8 encoding of https://github.com/dfinity/candid/blob/master/spec/Candid.md#core-grammar[the Candid interface] for the canister.
 
+* `/canister/<canister_id>/property/<name>` (blob):
++
+Canister administrators may set and update a list of named canister setting properties.
+
+The system may impose a size limit on the properties; it allows at least 4KB of combined size of the keys keys and values. Values can be empty.
+
+These properties are configured and kept independently from installing or uninstalling code.
+
+
 [#http-interface]
 == HTTPS Interface
 
@@ -1560,6 +1569,12 @@ Calls to a frozen canister will be rejected (like for a stopping canister). Addi
 +
 Default value: 2592000 (approximately 30 days).
 
+* `properties` (`vec record { name: text; value: blob; }`)
++
+A set of arbitrary named properties with arbitrary values. The names in the list must be free of duplicates. See `_state-tree-canister-information`.
++
+Default value: The empty list.
+
 
 [#ic-update_settings]
 === IC method `update_settings`