Add backward compatibility support for macsec keys with text string format

[judyjoseph]

To do the following to support backward compatibility for macsec CAK primary and fallback keys: > Add a config_db attribute to control the key type if it is text based or type 7 > Add a knob in CLI for user to specify it is text based or type 7

This will be a new requirement, since 202205 is not deployed widely the backward compatibility is not a critical requirement.

Another option for this is to let user give input as plain text/type7 encoded -- but store in type7 format always in config_db.