Fix encoding issues when reading emails using the email plugin

[sdelgadoc]

Fix encoding issues when reading emails in the email plugin

• Identify encoding problems in email subject and body text
• Handle encoding issues elegantly if they are found
• Added comments to highlight functionality added

The previous version of the email plugin was encountering encoding errors when reading emails, as documented in the following issues (https://github.com/Significant-Gravitas/Auto-GPT-Plugins/issues/104, https://github.com/Significant-Gravitas/Auto-GPT-Plugins/issues/110). This PR attempts to resolve as many of the encoding issues as I was able to identify.

[ntindle]

Thanks! Can you add a matching test?

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.18 :warning:

Comparison is base (57d9213) 67.21% compared to head (8114a4f) 67.04%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #139      +/-   ##
==========================================
- Coverage   67.21%   67.04%   -0.18%     
==========================================
  Files          21       27       +6     
  Lines        1458     1681     +223     
  Branches      180      188       +8     
==========================================
+ Hits          980     1127     +147     
- Misses        462      534      +72     
- Partials       16       20       +4     

see 6 files with indirect coverage changes

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[sdelgadoc]

Add tests

Added tests per request from @ntindle