MINOR: jwt: Add new "add/del/show ssl jwt" CLI commands

MINOR: jwt: Add new "add/del/show ssl jwt" CLI commands

The new "add/del ssl jwt <file>" commands allow to change the "jwt" flag
of an already loaded certificate. It allows to delete certificates used
for JWT validation, which was not yet possible.
The "show ssl jwt" command iterates over all the ckch_stores and dumps
the ones that have the option set.