Configurable TopologyValidator plugin mechanism

[LeonardoBonacci]

By solving this issue, this PR also introduces some configurable flexibility in the validator 'framework'. It allows a potential String parameter to be inserted in the constructor by naming convention (# is used as a separator in this example). It can then be used in the corresponding TopologyValidatorImpl at will.

It's backwards compatible.

Still work in progress. Feedback is welcome and community acceptance is required before proceeding.

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[LeonardoBonacci]

Great ideas, thanks for that!
For the sake of communication I have implemented and committed your suggestions.

The TopologyValidator change is reverted and the TopicNameRegexValidation takes its argument(s) from the config, like this:
topology.validations.0=com.purbon.kafka.topology.validation.topology.TopicNameRegexValidation
topology.validations.regexp=foo.bar.[a-zA-Z]+.[a-zA-Z]+

One thing to notice though is that you suggested to add the regex in the config topology.validations.regexp.0
With the implemented decoupling and the possibility to chain Validators it is not certain to be validation 0 (it might as well be 1, 2, etc.). Therefore I have used (and this is up to the developer of each Validator), a generic config path without the numerical component topology.validations.regexp

No need to take the PR yet - if everyone agrees I will make a clean commit without the intermediate commits of this branch.

[purbon]

Hi, quick question, could it happen for a user to have the need of more than one regexp to validate topics? a fair answer would it be that not, so we only have one regular expression and one topic name validator. What do you think?

If that would be the case, do you think we could add a validation for this config, a check like if you tried to have more than one TopicNameRegexValidation, raise an exception. Does this make sense?

[purbon]

On the other side, before we merge this in, would you please be so nice to add a few notes (does not need to be a bible 😄 ) in the documentation about it? thanks a lot.

[purbon]

I really like where this is going! thanks a lot for your help here @LeonardoBonacci !! really appreciated

[LeonardoBonacci]

PR in progress

[purbon]

Hi @LeonardoBonacci, do you mind adding test for the validation?

[purbon]

Hi @LeonardoBonacci, if you don't mind I would import these changes within #274, add test and add it to master! thanks a lot for your contribution.