chore: allow disabling browser sandbox

[VerteDinde]

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• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
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Summarize your changes:

Resolves #74

This PR does not force the browser-sandbox interface to true. Having this sandbox requires a manual review in the Snap store, and is not used by many large Electron apps. In strict confinement mode, Electron apps can instead use the snap's confinement.

We'll be moving the template from a default of classic to strict in the future, but this change will allow apps to build for the snap store and pass review without manual changes.

[welcome]

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[codecov]

Codecov Report

Merging #141 (53dd0be) into master (49da95d) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

❗ Current head 53dd0be differs from pull request most recent head 91afcf0. Consider uploading reports for the commit 91afcf0 to get more accurate results

@@            Coverage Diff             @@
##           master     #141      +/-   ##
==========================================
- Coverage   95.65%   95.61%   -0.04%     
==========================================
  Files           8        8              
  Lines         253      251       -2     
==========================================
- Hits          242      240       -2     
  Misses         11       11              

Impacted Files	Coverage Δ
src/yaml.js	100.00% <100.00%> (ø)

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