Cleanup DataType

[richardstartin]

Cleans up the DataType enum which I noticed could be simplified while investigating another issue.

[snleee]

LGTM. This looks much cleaner.

[codecov-commenter]

Codecov Report

Merging #8214 (d44bbfc) into master (916d807) will decrease coverage by 8.38%.
The diff coverage is 91.89%.

@@             Coverage Diff              @@
##             master    #8214      +/-   ##
============================================
- Coverage     71.02%   62.64%   -8.39%     
+ Complexity     4314     4232      -82     
============================================
  Files          1626     1614      -12     
  Lines         84929    84634     -295     
  Branches      12783    12749      -34     
============================================
- Hits          60325    53015    -7310     
- Misses        20462    27724    +7262     
+ Partials       4142     3895     -247     

Flag	Coverage Δ
integration1	28.69% <0.00%> (-0.10%)	⬇️
integration2	?
unittests1	67.34% <91.89%> (-0.05%)	⬇️
unittests2	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...main/java/org/apache/pinot/spi/data/FieldSpec.java	82.41% <91.89%> (+1.02%)	⬆️
...t/core/plan/StreamingInstanceResponsePlanNode.java	0.00% <0.00%> (-100.00%)	⬇️
...pinot/controller/recommender/io/ConfigManager.java	0.00% <0.00%> (-100.00%)	⬇️
...ore/operator/streaming/StreamingResponseUtils.java	0.00% <0.00%> (-100.00%)	⬇️
...troller/recommender/io/metadata/FieldMetadata.java	0.00% <0.00%> (-100.00%)	⬇️
...roller/recommender/rules/impl/BloomFilterRule.java	0.00% <0.00%> (-100.00%)	⬇️
...oller/api/resources/PinotControllerAppConfigs.java	0.00% <0.00%> (-100.00%)	⬇️
...ler/recommender/data/generator/BytesGenerator.java	0.00% <0.00%> (-100.00%)	⬇️
...ager/realtime/PeerSchemeSplitSegmentCommitter.java	0.00% <0.00%> (-100.00%)	⬇️
...er/recommender/io/metadata/SchemaWithMetaData.java	0.00% <0.00%> (-100.00%)	⬇️
... and 284 more

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