Add option to disable onion service

[waybackarchiver]

Description

To disable the onion service, set the WAYBACK_ONION_DISABLED environment variable. This feature will be supported in the next release or in the latest commit after this pull request is merged.

Close #370

Checklist

• I have followed the contributing guidelines
• I have reviewed and understood the Code of Conduct
• I have searched and make sure there's no duplicate PRs

[codecov]

Codecov Report

Patch coverage: 64.51% and no project coverage change.

Comparison is base (5fe18b7) 47.19% compared to head (d67c2d7) 47.19%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #372   +/-   ##
=======================================
  Coverage   47.19%   47.19%           
=======================================
  Files          58       58           
  Lines        5130     5136    +6     
=======================================
+ Hits         2421     2424    +3     
- Misses       2449     2450    +1     
- Partials      260      262    +2     

Impacted Files	Coverage Δ
service/httpd/httpd.go	72.88% <0.00%> (ø)
service/httpd/onion.go	6.15% <10.00%> (ø)
config/options.go	93.71% <100.00%> (+0.01%)	⬆️
config/parser.go	91.84% <100.00%> (+0.07%)	⬆️

... and 2 files with indirect coverage changes

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