fix: persist scheduler-k3s annotations and labels as JSON maps

Annotation and label values containing a newline previously round-tripped
as two adjacent `key: value` lines, and the second line then failed the
`SplitN(line, ": ", 2)` parse on read. Move the per-`(processType,
resourceType)` files to `PropertyMap*` storage so `\n` in values and `/`
in keys are preserved verbatim. An idempotent `TriggerInstall` migration
walks `--global` and every app, converting any legacy line-formatted file
in place by probing `PropertyMapGet` first and rewriting via
`PropertyListGet` only when the probe fails. Property names are
unchanged, so the annotations/labels report scanner and the
`reservedAnnotationPrefixes` filter keep working without modification.

Closes #8719.

docs/deployment/schedulers/k3s.md

@@ -376,6 +376,8 @@ The following resource types are supported:
 - `traefik_ingressroute`
 - `traefik_middleware`
 
+Annotation keys may contain `/` (e.g. Kubernetes-style keys such as `prometheus.io/scrape`) and values may span multiple lines; both are preserved verbatim.
+
 A `ps:restart` is required after setting annotations in order to have them apply to running resources.
 
 #### Removing an annotation
@@ -446,6 +448,8 @@ The following resource types are supported:
 - `traefik_ingressroute`
 - `traefik_middleware`
 
+Label keys may contain `/` (e.g. Kubernetes-style keys such as `app.kubernetes.io/part-of`) and values may span multiple lines; both are preserved verbatim.
+
 A `ps:restart` is required after setting labels in order to have them apply to running resources.
 
 #### Removing a label