[FLINK-6848] Update managed state docs

[Fokko]

Hi guys,

I would like to add an example of how to work with managed state in Scala. The code is tested locally and might be a nice addition to the docs.

Cheers,
Fokko Driesprong

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[tzulitai]

Hi @Fokko, thanks a lot for this contribution!

The current changes look good. However, while you're on it, what do you think about also adding a Scala counterpart example for the other code snippets on the page (e.g. managed operator state, source functions)?

The changes right now are good as is, but I prefer not to merge a "partially documented Scala example", which may give the wrong impression that Scala works only for some cases. What do you think?

[Fokko]

Hi @tzulitai,

I fully agree. Give me some time to work on the other Scala examples, I need to make sure that they are working properly. I'll wrap it up this week. I'll update the commit and rebase with master.

Cheers, Fokko

[Fokko]

Hi @tzulitai,

I've added some more Scala examples. If you are still missing something, please let me know.

Kind regards, Fokko

[tzulitai]

Thanks a lot @Fokko! This looks very good. +1.

Merging this ...