Updated QPS and Burst capacity for k8s client

[abheda-crest]

The PR focuses on updating QPS and Burst capacity for k8s client to handle a higher frequency of SA token retrieval. These configurations are now set via environment variables in deployment config, providing flexibility for adjusting values as per requirement. Additionally, the load test has been updated to reflect these changes.

Related to: #198 & #383

Example (deploy/provider-gcp-plugin.yaml):

          env:
            - name: TARGET_DIR
              value: "/etc/kubernetes/secrets-store-csi-providers"
            - name: K8S_CLIENT_QPS
              value: "20.0"
            - name: K8S_CLIENT_BURST
              value: "50"

Tested in the GKE environment across various configurations demonstrated successful scaling under moderate loads.
For ~100 secrets, the GKE environment remained stable across all tested pod and node configurations, supporting ~300 pods without issues.