Support for multiple comma separated values / file for allow / deny flag

[ehsandeep]

Is your feature request related to a problem? Please describe.
httpx supports allow/deny flag to define IPs/CIDRs to process, currently, it's limited to a single value per flag, for passing multiple values, the same flag needs to be used multiple times, this support can be enhanced by adding comma-separated values or file as if possible with the same flag.

We have similar support in dnsx for r flag to feed file or multiple comma-separated values.

  -r string
    	List of resolvers (file or comma separated)

Describe the solution you'd like

echo http://localhost | httpx -probe -deny 127.0.0.0/8,10.0.0.0/8,1.1.1.1
echo http://localhost | httpx -probe -allow 127.0.0.0/8,10.0.0.0/8,1.1.1.1
echo http://localhost | httpx -probe -allow allow-list.txt
echo http://localhost | httpx -probe -deny deny-list.txt

Related issue:- #371