docs: add help, update docs for env:list --json flag

[tinfoil-knight]

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Summary

The --json flag is added to the base command but help output is hidden from users by default since all commands don't support this option.

The help output should be visible for the env:list command.

Note: Reported by users (#3262 (comment)) & @verythorough (#3262 (comment)).

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[github-actions]

📊 Benchmark results

Comparing with 3f3f9c9

Package size: 259 MB

(no change)

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Legend

• T-30 (a49e5fc): 249 MB
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• T-12 (12664f3): 249 MB
• T-11 (7ebf238): 249 MB
• T-10 (df9260a): 249 MB
• T-9 (e3db314): 249 MB
• T-8 (7eb4479): 249 MB
• T-7 (89b14e2): 249 MB
• T-6 (e1f661a): 242 MB
• T-5 (2994d3e): 259 MB
• T-4 (aa3939a): 259 MB
• T-3 (61675b2): 259 MB
• T-2 (2f1f8fd): 259 MB
• T-1 (3f3f9c9): 259 MB
• T (current commit): 259 MB

[tinfoil-knight]

Some other commands: env:get, env:import, env:set, env:unset, sites:create-template, sites:create, status also support JSON output but don't say so in their help output or in the docs. Should I update those too?

[verythorough]

Ah, sorry I missed this earlier! LGTM!