Add exclude-hostname-length flag to dynamically adjust exclude-length

[0xyy66]

This PR introduces the --exclude-hostname-length flag for the vhost option to Gobuster, allowing users to dynamically adjust the exclude-length value based on the length of the hostname (fuzzing word) in the response. This feature is useful for cases where webservers return the subdomain or hostname in the response, causing the response length to vary.

Key Changes:

• New vhost flag --exclude-hostname-length
• Simple change in exclude length control logic: if (found && !v.options.ExcludeLengthParsed.Contains(int(size)-wordLength)) (subtracts the hostname length from the returned size, always matching the static size entered by the user)

PoC

In the following screenshot, the response size is variable because of the subdomain included in the response. The problem could be bypassed by submitting a range but it would be less precise.

By submitting the static size to --exclude-length (283 in this case) and the --exclude-hostname-length flag, Gobuster skips all the previous false positives.