VAULT_SECRET_DATA_JSON to output just secret JSON object

[robertlestak]

This adds a new optional environment variable VAULT_SECRET_DATA_JSON (boolean true / false, default false).

If set to true, the extension will write just the secret.Data JSON, rather than the full api.Secret object with the nested Data field.

This is useful where the JSON object in Vault must be consumed as-is, such as with GCP Service Accounts.

[hashicorp-cla]

All committers have signed the CLA.