fix: Reject zero and empty values admission used to let through

[as51340]

Why

Follow-up to #72's API audit: "if you really want to disallow zero values or empty strings for a field, use MinLength=1 / Minimum=1". Four fields accepted a value that only failed after admission (as ApplyFailed or a pod that never starts), or that silently meant something else.

What

Field	Accepted	What happened	Now
monitoring.vmagentRemote.scrapeInterval	"" (every unit in the duration pattern is optional)	Stored as "", because a schema default only fills a missing field; the builder then quietly used 15s	MinLength=1
securityContext.runAsUser	0	The Memgraph container sets runAsNonRoot, so the kubelet refuses to start it	Minimum=1 (runAsGroup/fsGroup keep 0, a legitimate gid)
coreDumps.uploader.envFromSecrets[]	anything, including ""	Became secretRef.name, so the StatefulSet apply failed with ApplyFailed	Same MinLength/MaxLength/DNS-subdomain rules as every secretName
storage.<role>.libPVCSize, coreDumps.<role>.size	0, -1Gi at creation (the existing rules only block a shrink)	The claim template was refused at apply time	CEL: must be greater than zero

Left alone on purpose: the storage class names ("" disables dynamic provisioning, as documented), EnvVar.value, FlagValue, the uploader's command/args items, and priorityClassName/serviceMonitor.interval (optional, where "" already means unset).

Compatibility: this only tightens validation. An existing object holding one of these values fails its next update until it is corrected; nothing changes for valid objects or their pods.

Chart version 1.0.1-rc.1 → 1.0.1-rc.2 for the CRD change. #72 makes the same bump, so whichever merges second needs rc.3.

Testing

• New envtest rejection cases for each field: root uid, zero lib claim, negative core dumps claim, empty and non-DNS uploader Secret, and a blanked-out scrape interval sent as a raw manifest (the typed client drops ""). The raw manifests now share a rawCluster helper.
• make test, make lint, make chart-verify, make helm-lint, make chart-version-check.