[WIP] Django compatible

[waketzheng]

Description

Make it easy to migrate models from Django

Motivation and Context

When the first time I used tortoise-orm, I quite not understand why using DatetimeField/ForeignKeyField, why not just DateTimeField/ForeignKey like Django.
Now I think that we can support both of them.

How Has This Been Tested?

make ci

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codspeed-hq]

CodSpeed Performance Report

Merging #2030 will not alter performance

_{Comparing waketzheng:django-compatible (d667a6d) with develop (752762c)}

Summary

✅ 16 untouched

[coveralls]

Pull Request Test Coverage Report for Build 19983184978

Details

• 30 of 34 (88.24%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.07%) to 90.651%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
tortoise/fields/base.py	6	10	60.0%

Totals
Change from base Build 19726043557:	-0.07%
Covered Lines:	6661
Relevant Lines:	7229

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💛 - Coveralls