fix(kafka): bump default resourcesPreset to medium - #2537

…dium (#2589)

# Description
Backport of #2537 to `release-1.3`.

## What this PR does

The barman-cloud plugin injects its sidecar with no resource requests or
limits. What that means depends on the namespace. A tenant with
`resourceQuotas` set ships a `LimitRange` that defaults containers to
128Mi (`packages/apps/tenant/templates/quota.yaml`), so there the
sidecar inherits that default and is OOMKilled mid-backup. A namespace
without a `LimitRange`, which is `cozy-keycloak` and any tenant that
leaves `resourceQuotas` empty, gave the sidecar no requests and no limit
at all, so nothing reserved memory for it and nothing bounded it. The
failure on the tenant path is quiet from the control plane: the
`ObjectStore` stays healthy, the `Cluster` stays `Ready`, and only the
backup fails.

Observed on a 1.6 cluster while backing up a 38 MB database:
`lastState.terminated.reason: OOMKilled`, `exit 137`, four restarts on
the sidecar, and a cgroup high-water mark of 254 MiB.
`container_memory_working_set_bytes` peaked at only 64 MiB over the same
window — it is sampled, and it misses the spike that actually triggers
the kill, which is why the working-set number does not explain the
failure on its own.

Both paths that build an ObjectStore now carry resources:

- `cozy-lib.barman.sidecarConfiguration`, used by
`packages/apps/postgres` for the backup and recovery ObjectStores and by
`packages/system/keycloak`;
- `barmanSidecarConfiguration()` in
`internal/backupcontroller/cnpgstrategy_controller.go`, which builds the
platform's own ObjectStore on the `useSystemBucket=true` path.

Requests are 100m/256Mi with a 1Gi memory limit on every caller: 256Mi
holds the measured working set and 1Gi is four times the measurement,
which is also the ceiling a caller without a LimitRange gets where it
had none. No CPU limit is set, following the `entityOperator` precedent
in `packages/apps/kafka/templates/kafka.yaml`: a throttled sidecar
stalls WAL archiving instead of failing it, which is harder to notice
than an outright failure. Measured CPU peak was 50 mCPU. Inside a tenant
the limit is charged against the `ResourceQuota` `limits.memory` budget,
1Gi per instance pod; a 4Gi tenant spends a quarter of it per Postgres
instance.

The helper is renamed from `checksumSidecarConfiguration` to
`sidecarConfiguration`, because it no longer carries only the checksum
pin and its name and doc comment would otherwise be wrong.

Tests cover both paths and both render sites: a new helm suite in
`packages/apps/postgres`, extra assertions in the existing keycloak
suite, an assertion in the controller test, and a deepcopy test for the
new field. Each of them fails against the unfixed sources.

One thing this PR deliberately does not do. This is the fifth time the
128Mi tenant default has been worked around per component — kafka and
zookeeper presets (#2537), the kafka entity-operator (#2934), the
cert-manager cainjector (#3199), and the note carried in the
etcd-operator values. Whether the default itself should move looks like
your call rather than something to fold into a fix for one sidecar, so
it is left alone here.

### Screenshots

Not a UI change.

### Downstream repositories

Walked the trigger map in `docs/agents/contributing.md` against the
diff, entry by entry. The change touches one cozy-lib helper, the two
chart templates that include it, one Go function, and tests. It adds,
renames or removes no package; changes no `values.yaml`,
`values.schema.json`, `Chart.yaml` or `README.md`, so no version enum,
default or generated artifact moves; changes no `ApplicationDefinition`
semantics, no `release.prefix`, no output Secret or Service name;
touches no CRD, no namespace, no `hack/` file, no telemetry metric or
label, no `cozy-proxy` annotation, no node or network requirement, and
no commit or PR convention. No entry matches.

- [x] No downstream repository is affected by this change

### Release note

```release-note
fix(backups): give the barman-cloud sidecar its own resources
The barman-cloud sidecar was injected without resource requests or limits, so in tenant namespaces it inherited the 128Mi `LimitRange` default and was OOMKilled during backups while the `ObjectStore` and the `Cluster` both stayed healthy. It now requests 100m/256Mi and caps memory at 1Gi on the chart path and on the platform's Go path alike; in namespaces without a LimitRange the sidecar had no limit before and gets the same 1Gi ceiling.
```


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Added explicit CPU and memory resource settings for barman-cloud
backup and recovery sidecars.
- Backup sidecars request 100m CPU and 256Mi memory, with a 1Gi memory
limit.
  - Recovery sidecars receive a 1Gi memory limit.
  - Preserved the S3 checksum configuration.

- **Bug Fixes**
- Prevented sidecars from inheriting unsuitable tenant resource limits.
- Ensured resource settings are preserved when backup configuration is
copied.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->