Add new type to key-value converter

[zewditu]

We are excited to review your PR.

So we can do the best job, please check:

• [ ] There's a descriptive title that will make sense to other developers some time from now.
• [ ] There's associated issues. All PR's should have issue(s) associated - unless a trivial self-evident change such as fixing a typo. You can use the format Fixes #nnnn in your description to cause GitHub to automatically close the issue(s) when your PR is merged.
• [ ] Your change description explains what the change does, why you chose your approach, and anything else that reviewers should know.
• [ ] You have included any necessary tests in the same PR.

[codecov[bot]]

Codecov Report

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

Comparison is base (5e28578) 68.80% compared to head (4571677) 68.80%. Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6973 +/- ## ========================================== - Coverage 68.80% 68.80% -0.01% ========================================== Files 1249 1249 Lines 249686 249686 Branches 25485 25485 ========================================== - Hits 171806 171795 -11 - Misses 71286 71295 +9 - Partials 6594 6596 +2 ``` | [Flag](https://app.codecov.io/gh/dotnet/machinelearning/pull/6973/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | Coverage Δ | | |---|---|---| | [Debug](https://app.codecov.io/gh/dotnet/machinelearning/pull/6973/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `68.80% <100.00%> (-0.01%)` | :arrow_down: | | [production](https://app.codecov.io/gh/dotnet/machinelearning/pull/6973/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `63.27% <ø> (-0.01%)` | :arrow_down: | | [test](https://app.codecov.io/gh/dotnet/machinelearning/pull/6973/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `88.41% <100.00%> (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=dotnet#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/dotnet/machinelearning/pull/6973?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | Coverage Δ | | |---|---|---| | [test/Microsoft.ML.TestFramework/BaseTestClass.cs](https://app.codecov.io/gh/dotnet/machinelearning/pull/6973?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet#diff-dGVzdC9NaWNyb3NvZnQuTUwuVGVzdEZyYW1ld29yay9CYXNlVGVzdENsYXNzLmNz) | `88.23% <100.00%> (ø)` | | | [...osoft.ML.Tests/TrainerEstimators/TreeEstimators.cs](https://app.codecov.io/gh/dotnet/machinelearning/pull/6973?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet#diff-dGVzdC9NaWNyb3NvZnQuTUwuVGVzdHMvVHJhaW5lckVzdGltYXRvcnMvVHJlZUVzdGltYXRvcnMuY3M=) | `97.84% <ø> (ø)` | | ... and [3 files with indirect coverage changes](https://app.codecov.io/gh/dotnet/machinelearning/pull/6973/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet)