Add optional http2 input to enable HTTP/2 communication with Vault

[0xD3ADBE3F]

Description

Adds a new optional input http2 (default: false) to enable HTTP/2 when communicating with Vault. This allows multiplexed requests over a single connection, potentially improving performance and reducing latency for workflows interacting heavily with Vault, while remaining opt-in to preserve existing behavior.

Checklist

• Added CHANGELOG entry (only for user-facing changes)

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PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.

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