Add Python version in Developer README

[kevin1chun]

This change adds Python 3.10 to the Local Development README page. Currently, if Python 3.11+ is used then the build process fails.

> Task :metadata-ingestion:checkPythonVersion FAILED
Traceback (most recent call last):
  File "<string>", line 1, in <module>
AssertionError: Python version (3, 11) not allowed

Py3.7 and 3.10 are technically both valid (see: https://github.com/datahub-project/datahub/blob/master/.github/workflows/metadata-ingestion.yml#L34), however, 3.7 is already EOL.

I also added the pyenv local version config file to .gitignore since this popular tool allows developers to use pyenv to control their python version.

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[david-leifker]

Just let the tests run to merge. Typically doc only means they don't get run but the update to the gitignore triggered them so will let them go. Thanks!