* Add support for client certificates to -output-curl-string
I did not write tests for this feature as -output-curl-string was not
already tested and this is a simple change. Because the name of the
certificates would be lost once loaded I added fields to Config to keep
track of them. I did not add a public method for the user to set them
explicitely as I don't think anyone would need this functionnality
outside of the Vault CLI.
Closes https://github.com/hashicorp/vault/issues/13376
* Add changelog
* Add lock in ConfigureTLS
