feat: Added udf/udaf support to th etesting tool.

[hjafarpour]

Description

This PR adds UDF/UDAF support to the testing tool. I also removed some unused methods! It also fixes #3094

Testing done

Test with UDF added.

Reviewer checklist

• [ ] Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• [ ] Ensure relevant issues are linked (description should include text like "Fixes #")

[big-andy-coates]

Hey @vpapavas

I talked to @apurvam and we thought you might be able to pick up this PR and see it through...?

[big-andy-coates]

Linking to #2804, which is the ticket that #3094 was closed as a duplicate of

[holgerbrandl]

UDF support is key to efficiently use the ksql-test-runner. Any news on this subject? Or is there any workaround to do so?

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