chore(docs): add java examples and ci tests

[slbotbm]

closes #1893

[slbotbm]

A few questions:

1. The getting-started and basic examples are pretty similar - they only have the batch_limit and messages_per_batch different.
2. The async example in foreign/java/examples still exists. Should that be moved here?

[hubcio]

@slbotbm

1. lets remove basic then
2. yes

[slbotbm]

The latest commit adds the async examples to examples/java and deletes the foreign/java/examples directory. Also removes the basic example

[hubert-laserdata]

let's wait for @mmodzelewski review, also maybe @chiradip has any comments :)

[chiradip]

I will have a look.

[mmodzelewski]

Hey @slbotbm, thanks a lot for the PR! It looks great, I added just a few minor comments. Please have a look at them and once resolved we'll be able to merge the PR :)

[mmodzelewski]

@slbotbm Many thanks for the contribution. Great work!

[slbotbm]

@hubcio @mmodzelewski Thank you for your constructive comments and guidance, and for making my first contribution experience pleasant; looking forward to collaborating and contributing to iggy!