expose Memgraph snapshot interval/retention/on-exit

[nimisha-gj]

Problem

Memgraph takes a periodic snapshot every 300s by default — this comes from the image's /etc/memgraph/memgraph.conf (--storage-snapshot-interval-sec=300), entirely inside the Memgraph
process. The operator builds the Memgraph command line in buildMemgraphArgs but passes no snapshot-related flags, so there was no way to tune or disable this behavior through the
MemgraphCluster CRD.

In production this caused an outage: a replica accumulated ~9.3 GB of snapshots on a 10 GB volume, hit 100% disk, and Memgraph then crash-looped on startup because RocksDB couldn't
initialize:
RocksDB couldn't be initialized inside /var/lib/memgraph/settings -- IO error: No space left on device
Note the existing SnapshotSpec (snapshot.enabled/schedule/retentionCount) only controls the operator's CronJob (CREATE SNAPSHOT) and the preStop hook — it does not touch Memgraph's
internal periodic snapshots, which are the real disk-filler. There was simply no knob for them.

Fix

Expose Memgraph's snapshot flags through MemgraphConfig so they can be tuned (or disabled) per cluster

• Fields are *int32/*bool pointers: nil means "leave Memgraph's default", so the change is fully backward compatible — existing clusters are unaffected until they set a value.
  Pointers also let 0/false be distinguished from unset (important, since 0 is the "disable" value).
• buildMemgraphArgs appends each flag only when the field is set.
• Regenerated CRD (config/crd/bases/...) and deepcopy via make generate manifests.

Usage

  spec:
    config:
      snapshotIntervalSec: 0      # disable periodic snapshots
      # or e.g. 3600 to snapshot hourly instead of every 5 min
      snapshotOnExit: false       # optional: also skip the shutdown snapshot

Testing

• go build ./... clean; make generate manifests produces no further diff.
• Added unit test TestBuildMemgraphArgsSnapshotFlags: verifies no snapshot flags are emitted when unset, interval=0 emits --storage-snapshot-interval-sec=0, and all three flags render
  when set. Existing TestBuildMemgraphArgs unaffected.

Notes / follow-ups

• Disabling snapshots entirely (snapshotIntervalSec: 0 + snapshotOnExit: false) leaves only WAL for durability — recovery from an unclean crash is limited. Prefer a non-zero interval
  (e.g. 3600) unless you have a specific reason to fully disable.
• The operator does not reconcile config changes onto an existing StatefulSet (only replicas/image), so applying a new value still requires a StatefulSet roll.
• Consumers (e.g. Helm charts) must pass this value through with a hasKey/explicit check, not | default — Go templates treat 0/false as empty and would drop the disable value.