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.yaml

@@ -212,7 +212,15 @@ garage:
   # Garage's defaults, exposed because they are the two knobs that trade disk
   # against CPU. blockSize is the chunk size objects are split into;
   # compressionLevel is the zstd level for stored blocks (1 = fast, higher =
-  # smaller, "none" is not a value here - set 0 to disable).
+  # smaller, negative levels are zstd's "fast" modes).
+  #
+  # TO DISABLE COMPRESSION, WRITE THE STRING "none" - and not 0, which is the
+  # trap this comment exists for: Garage's deserializer accepts an integer or
+  # the literal "none" (src/util/config.rs, deserialize_compression), and 0 is
+  # a perfectly valid integer that zstd reads as "use my default level", i.e.
+  # level 3 - MORE compression than the 1 below, not less. The schema therefore
+  # accepts an integer or exactly "none", and the ConfigMap quotes the string
+  # form so the rendered TOML stays valid.
   blockSize: "1M"
   compressionLevel: 1