Splitted 'io_json' feature flags in read/write

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02 :tada:

Comparison is base (eed5ebb) 83.70% compared to head (b2922f4) 83.73%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1487 +/- ## ========================================== + Coverage 83.70% 83.73% +0.02% ========================================== Files 389 389 Lines 41814 41814 ========================================== + Hits 35002 35013 +11 + Misses 6812 6801 -11 ``` | [Impacted Files](https://app.codecov.io/gh/jorgecarleitao/arrow2/pull/1487?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao) | Coverage Δ | | |---|---|---| | [src/io/json/read/mod.rs](https://app.codecov.io/gh/jorgecarleitao/arrow2/pull/1487?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao#diff-c3JjL2lvL2pzb24vcmVhZC9tb2QucnM=) | `100.00% <100.00%> (ø)` | | ... and [5 files with indirect coverage changes](https://app.codecov.io/gh/jorgecarleitao/arrow2/pull/1487/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao)

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