R4R: Bcrypt investigations / benchmarks

[cwgoes]

Closes #3547

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/)
• Added entries in PENDING.md with issue #
• rereviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[cwgoes]

Some decent resources on security parameter choice are here and here.

Based on reading those and our current threat model (only a process on the client's machine with access to ~/.gaiacli could copy the encrypted keys and try to brute force them), I think our current security parameter of 12, which takes about a quarter of a second to generate a key from a password, is sufficient for now.

(I've added this to a README.md in the associated directory for future reference)

[codecov]

Codecov Report

Merging #3638 into develop will decrease coverage by 0.29%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           develop   #3638     +/-   ##
=========================================
- Coverage    61.29%     61%   -0.3%     
=========================================
  Files          186     187      +1     
  Lines        13998   14065     +67     
=========================================
  Hits          8580    8580             
- Misses        4874    4941     +67     
  Partials       544     544

[jackzampolin]

Nice an clean 👌