Drop Python 3.7 support

Python 3.7 is now end of life - https://devguide.python.org/versions/#unsupported-versions

We should do the following:

Update release.yaml to use a more modern Python version

piccolo/.github/workflows/release.yaml

Line 17 in 36e80f5

python-version: 3.7
Update our CI scripts
- Remove 3.7 from python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
- Update if: matrix.python-version == '3.7' to if: matrix.python-version == '3.11'.
Update setup.py
- python_requires=">=3.7.0" -> python_requires=">=3.8.0"
  
  piccolo/setup.py
  
  Line 61 in 36e80f5
  
  python_requires=">=3.7.0",
- And drop this line:
  
  piccolo/setup.py
  
  Line 87 in 36e80f5
  
  "Programming Language :: Python :: 3.7",
Wherever we use from typing_extensions import Literal or from typing_extensions import Protocol we can now import them directly from the typing module instead. typing_extensions can then be moved from requirements.txt to test-requirements.txt.

The reason for dropping older versions is it makes our CI run faster, and we can adopt newer Python features without having to worry about backwards compatibility.

@dantownsend hey i would like to work on this issue
can you assign me thiss

@KekmaTime Cool, thanks!

@dantownsend i have done all the tasks mentioned in the tasklist. Let me know if there are any fixes i need to make.
Here is the link to the PR- #855

Resolved by #855