fix(garage): compressionLevel disables with "none", never with 0

My own values comment claimed 0 switches compression off. It does not:
Garage's deserializer takes an integer OR the literal string "none"
(src/util/config.rs, deserialize_compression), and 0 is a valid integer that
zstd reads as its default level - 3, i.e. MORE compression than the chart's 1,
not none. A comment that invites an operator to write 0 for "off" is the
values-that-must-not-lie shape with the lie in the documentation instead of in
the template.

The schema now accepts an integer (negative included, those are zstd's fast
modes) or exactly "none", and the ConfigMap quotes the string form so the
rendered TOML stays valid. Verified: 1, 7, -3 render unquoted, "none" renders
quoted and the result still parses as TOML, and any other string is rejected by
the schema.

No version bump: the chart is not published yet.

garage/values.schema.json

@@ -77,9 +77,11 @@
           "minLength": 1
         },
         "compressionLevel": {
-          "description": "zstd level for stored blocks; 0 disables compression.",
-          "type": "integer",
-          "minimum": 0
+          "description": "zstd level for stored blocks, or the literal string \"none\" to disable compression. NOT 0 for disabling: Garage accepts 0 as an integer and zstd reads it as its default level (3), i.e. more compression than 1, not none. Negative integers are zstd's fast modes.",
+          "oneOf": [
+            { "type": "integer" },
+            { "type": "string", "enum": ["none"] }
+          ]
         },
         "bindAddress": {
           "description": "Host part of the S3, web and RPC listeners. '[::]' accepts IPv4 as well while net.ipv6.bindv6only is 0.",