Allow for comments in IAM configuration files

Current situation

The trusted key authorization file, token authorization file, and authorization policy file allow for empty lines but do not allow for commented-out entries.

Desired outcome

A line with leading # character is recognized as a commented-out line, and is ignored. For example,

/etc/squashtf/trusted_key.pub,Main key,,"namespace-a,namespace-b"
#/etc/squashtf/another_key.pub,Secondary key,"a,b"

/etc/squashtf/yak.pub,Tertiary key

only defines two trusted keys, trusted_key.pub and yak.pub.