Add kraken2 datatype

[pvanheus]

The update in galaxyproject/tools-iuc#7257 for the kraken2 tool allows it to use a custom database passed as a parameter. Currently this uses the Directory datatype. This datatype allows a more specific input type to be specified and also allows a compressed archive to be uploaded and unpacked to the kraken2 database datatype.

How to test the changes?

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• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

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[mvdbeek]

I think there was some discussion about this already, but i think it'd be better to build an auto compressed version of Kraken2DatabaseDirectory instead ? We could also build an abstraction that allows just declaring the required files in the datatype config so we don't need code changes for this.

[pvanheus]

Some guidance on how to do this would be much appreciated!