Added support for JSON deserialization of string timestamps

[ayemjay]

Fixes #1456

[jorgecarleitao]

Beautiful PR! Thank you for this! 🙇

[codecov[bot]]

Codecov Report

Patch coverage: 97.05% and no project coverage change.

Comparison is base (73ed7c8) 83.45% compared to head (4409e1c) 83.45%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1457 +/- ## ======================================= Coverage 83.45% 83.45% ======================================= Files 376 376 Lines 41161 41193 +32 ======================================= + Hits 34350 34379 +29 - Misses 6811 6814 +3 ``` | [Impacted Files](https://codecov.io/gh/jorgecarleitao/arrow2/pull/1457?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/deserialize.rs](https://codecov.io/gh/jorgecarleitao/arrow2/pull/1457?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao#diff-c3JjL2lvL2pzb24vcmVhZC9kZXNlcmlhbGl6ZS5ycw==) | `74.03% <90.90%> (+0.40%)` | :arrow_up: | | [src/temporal\_conversions.rs](https://codecov.io/gh/jorgecarleitao/arrow2/pull/1457?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao#diff-c3JjL3RlbXBvcmFsX2NvbnZlcnNpb25zLnJz) | `90.94% <100.00%> (+0.71%)` | :arrow_up: | ... and [3 files with indirect coverage changes](https://codecov.io/gh/jorgecarleitao/arrow2/pull/1457/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao) Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jorge+Leitao)

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