Add support for using `tls.key`, `tls.crt` and `ca.crt` keys while
generating a Secret, using the `--tls-key-file`, `--tls-crt-file` and
`--ca-crt-file` flags respectively.
Mark the flags `--key-file`, `--cert-file` and `--ca-file` as
deprecated.

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>