Add Lower Bound for FastAPI Package

[stephen37]

Issue: #1010
This add a lower bound for the fastapi package. This is needed to avoid having poetry install a very old version of FastAPI (0.1.17) from Jan 2019.

After building MLServer locally with that change, when I installed it locally, you could see that we were using a more recent version of FastAPI

❯ poetry install
Installing dependencies from lock file

Package operations: 0 installs, 3 updates, 0 removals

  • Updating starlette (0.25.0 -> 0.22.0)
  • Updating fastapi (0.1.17 -> 0.89.1)
  • Updating mlserver (1.2.4 -> 1.3.0.dev3 /Users/stephenbatifol/Documents/wolt/code/fork_mlserver/dist/mlserver-1.3.0.dev3.tar.gz)

Then with Python

❯ python
Python 3.9.16 (main, Dec  7 2022, 10:02:13)
[Clang 14.0.0 (clang-1400.0.29.202)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import fastapi
>>> fastapi.__version__
'0.89.1'

I do wonder if we still need to have those constraints though, FastAPI solved and merged the problem that was present in 0.89.0