add samples for ZonedDateTime to api-infix

[robstoll]

Platform (all, jvm, js, android): all
Extension (none, kotlin 1.3): none

Code related feature

We also want to provide samples for the infix api

Following the things you need to do:

• copy apis/infix-en_GB/atrium-api-infix-en_GB-jvm/src/test/kotlin/ch/tutteli/atrium/api/infix/en_GB/samples/LocalDateTimeExpectationSamples.kt and rename to ZonedDateTimeExpectationSamples and adjust LocalDateTime to ZonedDateTime accordingly (see also ZonedDateTimeExpectationSamples in api-fluent)
• check that the sample in the KDoc Intellij is showing looks good (ALT+Mouse-click on function name) -- see ListExpectationSamples for how comments are written fir the infix API

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[iljakorneckis]

I'll work on this, if that's ok

[robstoll]

Sure 👍