DataGenerator readability improvements

[gregschohn]

Description

Rewrite the workload classes to use a fluent style w/ mixins so that the structure of what's being cons'ed together is much more immediately clear. Case in point, making the conversion took hours because 1) there weren't unit tests on the generator itself and 2) the one test that was there didn't have suitable logging - requests weren't printed out (which is probably why there what looked to be a bug in the docIds).

This also maintains the previous status-quo of the codebase in how to eschew static imports and shows how to favor mixins and for DSL-like (DSL-lite) applications.

• Category Refactoring
• Why these changes are required? First, to find out why there was pushback to removing static imports. Then I realized that I couldn't understand the code & decided that if this was going to be used more often, we needed it to be clearer and to have better patterns in place.
• What is the old behavior before changes and new behavior after changes? docIds no longer contain a space.

Issues Resolved

Same sonar cleanup as this PR, which was merged before this one was opened for review.

Testing

gradle testing

Check List

• [ ] New functionality includes testing
  • [x] All tests pass, including unit test, integration test and doctest
• [ ] New functionality has been documented
• [x] Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 80.67%. Comparing base (d90a448) to head (c5b7b0f). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1103 +/- ## ============================================ + Coverage 80.66% 80.67% +0.01% - Complexity 2892 2906 +14 ============================================ Files 383 384 +1 Lines 14359 14358 -1 Branches 989 989 ============================================ + Hits 11582 11584 +2 + Misses 2183 2181 -2 + Partials 594 593 -1 ``` | [Flag](https://app.codecov.io/gh/opensearch-project/opensearch-migrations/pull/1103/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opensearch-project) | Coverage Δ | | |---|---|---| | [gradle-test](https://app.codecov.io/gh/opensearch-project/opensearch-migrations/pull/1103/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opensearch-project) | `78.77% <100.00%> (+0.02%)` | :arrow_up: | | [python-test](https://app.codecov.io/gh/opensearch-project/opensearch-migrations/pull/1103/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opensearch-project) | `90.33% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opensearch-project#carryforward-flags-in-the-pull-request-comment) to find out more.

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