Add backup file adder code

[nrathaus]

Description

Add support such that when a file is found (200 HTTP OK code), additional extensions (related to backup files) are added to the queue

TODO

Some functionality is done quite ugly, let me know how you want to support it

1. backup extensions are hardcoded to a list, should I read it from a file? a config parameter?
2. _items is directly accessed, should I add a Dictionary func to add items? is it allowed to add to _items running it appears to have no ill effect

[NEX-S]

backup extensions are hardcoded to a list, should I read it from a file? a config parameter?
For the sake of extensibility, I think we should provide custom prefixes/suffixes using the parameter

[shelld3v]

Everything that's done behind the scenes must be known and decided by users, if you make a flag like --discover-backups I might consider it, even though I still don't think this is a good idea, because if you have found the file, why would you need the backup? And how many cases like this actually exist in the wild? Still appreciate it tho 🙏🏻

[NEX-S]

Everything that's done behind the scenes must be known and decided by users, if you make a flag like --discover-backups I might consider it, even though I still don't think this is a good idea, because if you have found the file, why would you need the backup? And how many cases like this actually exist in the wild? Still appreciate it tho 🙏🏻

when performing actual web page security checks, we often find that dynamic pages such as index.php and conn.php typically aren't parsed by middleware, which means we can't view their source code directly. If there is a backup version of these files, like conn.php.bak, we can successfully obtain the source code. Currently, we are unable to perform further detection on discovered files; instead, we simply append known file extensions to our dictionary, which is inefficient and results in a large number of HTTP requests being sent.

[iseries]

Why not using the suffix parameter? .bak,.BAK,.old (... and so in)

[NEX-S]

Why not using the suffix parameter? .bak,.BAK,.old (... and so in)为什么不使用后缀参数？ .bak,.BAK,.old（...等等）

this cause a lot http request to server. all we need is found index.php then try aceesss index.php.bak instead of try access index.php and index.php.bak

[iseries]

sed -E 's/(.*)/\1.bak\n\1.BAK\n\1.backup/' wordlist.txt > bak_wordlist.txt?

[nrathaus]

The idea is to find a file that exists, then see if .bak version of it exists - not to duplicate the number of files queried for by adding another extension