Update Slack Cookies bof to seach for user tokens in addition to cookies, and to have a settable max length for matches

[MayerDaniel]

Allows the slack cookies bof to hunt for user api tokens which can be used in conjuction with the user's cookie to query the slack API directly.

For example:

curl https://slack.com/api/users.list  -H "Authorization: Bearer xoxc-47..." -H "Cookie: d=xoxd-Xq45...(URL encoded)"

I also created a max length variable to limit string output for matches in memory that are missing a null terminated string