docs: use markdown instead of rst

[bednar]

Closes #634

Proposed Changes

Migrate README file from rst to markdown.

Updated docs:

• https://github.com/influxdata/influxdb-client-python/tree/readme-to-md?tab=readme-ov-file#influxdb-client-python
• https://influxdb-client--639.org.readthedocs.build/en/639/#

Checklist

• [x] CHANGELOG.md updated
• [x] Rebased/mergeable
• [x] pytest tests completes successfully
• [x] Commit messages are conventional
• [x] Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (7a5f655) 90.40% compared to head (fad3946) 90.40%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #639 +/- ## ======================================= Coverage 90.40% 90.40% ======================================= Files 39 39 Lines 3503 3503 ======================================= Hits 3167 3167 Misses 336 336 ```

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