Loki won't start if openstack swift storage is configured and swift user doesn't have permissions to create bucket

[piotrrotter]

Describe the bug
Loki won't start if openstack swift storage is configured and swift user doesn't have permissions to create bucket

Operation forbidden
error initialising module: ruler-storage
github.com/grafana/dskit/modules.(*Manager).initModule
        /src/loki/vendor/github.com/grafana/dskit/modules/modules.go:138
github.com/grafana/dskit/modules.(*Manager).InitModuleServices
        /src/loki/vendor/github.com/grafana/dskit/modules/modules.go:108
github.com/grafana/loki/v3/pkg/loki.(*Loki).Run
        /src/loki/pkg/loki/loki.go:458
main.main
        /src/loki/cmd/loki/main.go:129
runtime.main
        /usr/local/go/src/runtime/proc.go:271
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:1695

I believe this line is causing the problem: https://github.com/grafana/loki/blob/v3.1.1/pkg/storage/chunk/client/openstack/swift_object_client.go#L64

I could prepare a MR to fix this, but I don't want to make the decision on how to proceed.
Here are the solutions I see:

1. Do not attempt to create the bucket; only check if it exists or is writable.
2. Add a configuration parameter like CreateBucketIfNotExists, defaulting to true to preserve existing behavior.

To Reproduce
Steps to reproduce the behavior:

1. Started Loki (SHA or version) loki, version release-3.1.x-89fe788 (branch: release-3.1.x, revision: 89fe788d)
2. Started Promtail (SHA or version) N/A
3. Query: N/A

The Swift user doesn't have permission to create a bucket. Helm values:

       loki:
          storage:
            type: 'swift'
            swift:
              auth_version: 3
              internal: false
              auth_url: "{{ ocs_url }}"
              username: "{{ ocs_username }}"
              password: "{{ ocs_password }}"
              user_domain_name:  "{{ ocs_domain_name }}"
              project_id: "{{ ocs_project_id }}"
              region_name: "{{ ocs_region }}"
              container_name: "{{ ocs_bucket_name }}"
              max_retries: 5
              connect_timeout: 10s
              request_timeout: 10s

Expected behavior
Loki should not crash on startup if it doesn't have permission to create a bucket, assuming the bucket already exists.
For security reasons, it's not ideal to grant Loki these permissions.

Environment:

• Infrastructure: Kubernetes
• Deployment tool: helm