feat(helm): allow custom PV/PVC configuration in StatefulSet

[kataria1shivang]

What this PR does / why we need it:

This PR modifies the StatefulSet configuration in the single-binary Loki Helm chart to allow users to specify custom Persistent Volumes (PV) and Persistent Volume Claims (PVC) instead of the default automatic PV/PVC creation. This enhancement is particularly useful for environments like Amazon EKS, where custom storage classes or predefined PV/PVC configurations are required. Currently, the Helm chart automatically creates a PV/PVC, which may not meet the needs of all users, especially in environments that require custom storage configurations. This change adds the flexibility to specify user-defined PV/PVC, while maintaining the default behavior if no custom values are provided.

Notes:

• This update modifies the StatefulSet file to allow the customization of PV/PVC.
• It doesn’t require changes in values.yaml, but users can now specify their own PV/PVC by modifying the appropriate StatefulSet configuration.
• The default behavior (automatic PV/PVC creation) remains intact if users don’t specify custom values.
• This change has been verified and tested in Amazon EKS, ensuring the PV/PVC customization works as expected in cloud environments like EKS.

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