Encrypt cached sudo password

[TheTechromancer]

When not running as root, and when a password is required to sudo, bbot will cache the password so you don't have to repeatedly enter it during the scan. Whenever a process is executed that needs sudo privileges, the sudo password is inserted into its isolated environment, which is then passed to sudo using a custom askpass script.

This worked well but wasn't super secure, since it introduced the opportunity for a subprocess to snag your sudo password (accidentally or as part of telemetry collection, etc.).

For extra security, this PR encrypts the password using a randomly-generated 32-byte key which is discarded at the end of the scan.

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 48 lines in your changes missing coverage. Please review.

Project coverage is 93%. Comparing base (bac9442) to head (b991724).
Report is 30 commits behind head on dev.

Files with missing lines	Patch %	Lines
bbot/core/helpers/depsinstaller/sudo_askpass.py	0%	29 Missing ⚠️
bbot/core/helpers/depsinstaller/installer.py	55%	19 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##             dev   #1740   +/-   ##
=====================================
- Coverage     93%     93%   -0%     
=====================================
  Files        343     343           
  Lines      26177   26228   +51     
=====================================
+ Hits       24122   24136   +14     
- Misses      2055    2092   +37     

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