Enable strict-boolean-expressions lint rule

[cmdcolin]

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See https://typescript-eslint.io/rules/strict-boolean-expressions

would try to catch issues where you need to be more explicit about comparisons against undefined

motivated by #4234 where there were some number|undefined being used but if number was 0, it was falsy and didn't display

note that the default settings of this rule creates 1711 issues on our codebase. could review all the options of the rule to see if any are more suitable for our uses