add samples for collectionAssertions of 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 CollectionAssertionsSample from fluent-api, adjust imports ...api.fluent... to ...api.infix... and ajdust the samples accordingly (always use the infix syntax, never the fluent).
• check that the sample in the KDoc Intellij shows looks good (ALT+Mouse-click on function name)

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[Efpkaf]

I'll work on this

[robstoll]

@Efpkaf do you need help?

[szatyinadam]

I am working on this.