Add no_store_metadata support for KVV2 and PKI benchmark tests

[markcarriedo]

Summary

• Adds no_store_metadata config option to KVV2 benchmark tests; when enabled, the KV secrets engine is configured with no_store_metadata: true at setup
• Adds no_store_metadata field to PKI issue and sign role configs, passed through to Vault's role configuration
• Includes unit tests and fixture configs for KVV2 no_store_metadata, plus updated docs for all three test types

Test Plan

• go test ./... passes (verified locally)
• KVV2 benchmark runs correctly with no_store_metadata = true in config
• PKI issue/sign benchmarks accept no_store_metadata in role config without error

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