[feat] Provide explicit col dtypes from user side

[nabenabe0928]

This PR addresses the Issue#394.

Types of changes

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Note that a Pull Request should only contain one of refactoring, new features or documentation changes.
Please separate these changes and send us individual PRs for each.
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Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

Description

Motivation and Context

How has this been tested?

[codecov]

Codecov Report

Merging #396 (2d9f4f4) into development (1b8e76a) will decrease coverage by 0.08%.
The diff coverage is 84.88%.

@@               Coverage Diff               @@
##           development     #396      +/-   ##
===============================================
- Coverage        83.45%   83.37%   -0.09%     
===============================================
  Files              163      163              
  Lines             9637     9680      +43     
  Branches          1689     1683       -6     
===============================================
+ Hits              8043     8071      +28     
- Misses            1113     1128      +15     
  Partials           481      481              

Impacted Files	Coverage Δ
autoPyTorch/data/tabular_feature_validator.py	87.91% <80.48%> (-4.22%)	⬇️
autoPyTorch/data/utils.py	89.15% <86.66%> (-2.15%)	⬇️
autoPyTorch/data/base_feature_validator.py	100.00% <100.00%> (ø)
autoPyTorch/data/base_target_validator.py	97.91% <100.00%> (-0.05%)	⬇️
autoPyTorch/data/tabular_target_validator.py	92.92% <100.00%> (-0.13%)	⬇️
autoPyTorch/utils/common.py	90.12% <100.00%> (+0.25%)	⬆️
...essing/feature_preprocessing/RandomKitchenSinks.py	91.17% <0.00%> (-2.95%)	⬇️
...ipeline/components/setup/network_backbone/utils.py	87.12% <0.00%> (-1.52%)	⬇️
...nts/setup/network_backbone/ConvNetImageBackbone.py	100.00% <0.00%> (+3.84%)	⬆️

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[ravinkohli]

Closing this PR as it's gone stale and a new PR #441 has been created in lieu.