Extend all the examples

[b1ron]

This is to unify all examples and also add more commands for more coverage.

Tasks

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1. Extend functionality of the dotnet-example dotnet-example#5
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2. Extend functionality of the java-example java-example#3
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3. Extend functionality of the python-example python-example#2
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[AlekSi]

#554 is not merged and actually fails

[b1ron]

I have reverted FerretDB/java-example/pull/4.

The result from the dropDatabase command differs depending on whether the database exists or not. MongoDB just returns { "ok" : 1 } regardless. I must have created the test database leading me to create FerretDB/java-example/pull/4 as a "fix".

byron@byron-ThinkCentre-M910q:~/workdir/dance$ mongo --quiet --eval 'db.runCommand({dropDatabase: 1});'
{ "ok" : 1 }
byron@byron-ThinkCentre-M910q:~/workdir/dance$ mongo --quiet --eval 'db.foo.insert({}); db.runCommand({dropDatabase: 1});'
{ "dropped" : "test", "ok" : 1 }