feature: add custom retention periods for data

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

Allows for custom data retention ranges by setting either --retention or the retention field in the config flags. This supports a human-readable time (e.g. 5m, 1d).

Issue

If applicable, what issue does this address?

Closes: #239

Testing

If relevant, please state how this was tested. All changes must be tested to work:

If this is a code change, please also indicate which platforms were tested:

• Windows
• macOS
• Linux

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov-commenter]

Codecov Report

Base: 18.43% // Head: 18.50% // Increases project coverage by +0.07% 🎉

Coverage data is based on head (77cdfee) compared to base (97bf8bf).
Patch coverage: 63.15% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #892      +/-   ##
==========================================
+ Coverage   18.43%   18.50%   +0.07%     
==========================================
  Files          74       74              
  Lines       13798    13820      +22     
==========================================
+ Hits         2543     2558      +15     
- Misses      11255    11262       +7     

Impacted Files	Coverage Δ
src/app.rs	0.00% <0.00%> (ø)
src/constants.rs	0.00% <ø> (ø)
src/bin/main.rs	37.43% <33.33%> (ø)
src/options.rs	42.66% <69.09%> (+0.14%)	⬆️
src/clap.rs	100.00% <100.00%> (ø)

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