Vault location (starting point to find the vault).
To create a vault, use create_vault() or create_package_vault().
If this is NULL, then secret tries to find the vault automatically:
If the secret.vault option is set to path, that is used as the
starting point.
Otherwise, if the R_SECRET_VAULT environment variable is set to a
path, that is used as a starting point.
Otherwise the current working directory is used as the starting
point.
If the starting point is a vault, that is used. Otherwise, if the
starting point is in a package tree, the inst/vault folder is used
within the package. If no vault can be found, an error is thrown.