Add tags_JSON to BackendEntityView and SpanEventView

[suddendust]

• Leaves tags as is because tags__KEYS and tags__VALUES are derived from this column.
• Both of these columns are still needed for running LIKE and IN queries on Explorer.
• tags_json is a string serialised as a JSON string. The corresponding datatype in Pinot is JSON.
• We'll run only CONTAINS_KEY and EQUALS queries on this column, as there's no way to run these queries using the json index natively.

[codecov]

Codecov Report

Merging #125 (95a5c32) into rzp_main (fbbd57d) will decrease coverage by 0.02%.
The diff coverage is 93.05%.

@@              Coverage Diff               @@
##             rzp_main     #125      +/-   ##
==============================================
- Coverage       80.69%   80.66%   -0.03%     
  Complexity       1359     1359              
==============================================
  Files             120      120              
  Lines            5345     5353       +8     
  Branches          495      495              
==============================================
+ Hits             4313     4318       +5     
- Misses            808      811       +3     
  Partials          224      224              

Flag	Coverage Δ
unit	80.66% <93.05%> (-0.03%)	⬇️

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Impacted Files	Coverage Δ
...ewgenerator/generators/SpanEventViewGenerator.java	90.71% <92.85%> (-1.83%)	⬇️
...nerator/generators/BackendEntityViewGenerator.java	89.85% <100.00%> (+0.14%)	⬆️
...ce/viewgenerator/generators/BaseViewGenerator.java	81.81% <100.00%> (+0.56%)	⬆️

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[github-actions]

Unit Test Results

  78 files  ±0    78 suites  ±0   59s ⏱️ -1s
405 tests +1  405 ✔️ +1  0 💤 ±0  0 ❌ ±0 

Results for commit 95a5c32. ± Comparison against base commit fbbd57d.