Convert TranslationSets to json

[stefanhaller]

• PR Description

This lays the ground for translating lazygit's texts using a translation system such as Crowdin, Weblate, or Poeditor.

See #3070.

[codacy-production]

Coverage summary from Codacy

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Coverage variation	Diff coverage
Report missing for 2ccd9981	✅ 21.21%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (2ccd998)	Report Missing	Report Missing	Report Missing
Head commit (741d9a2)	48590	41482	85.37%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3649)	66	14	21.21%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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Footnotes

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[jesseduffield]

LGTM. I'm glad we can still update the english stuff in a Go struct (so that I don't need to involve another file when making a change)