Fastapi-opa

- Update dependencies due to vulnerabilities
- [certifi](https://github.com/advisories/GHSA-xqr8-7jwr-rhp7)
- [cryptography](https://github.com/advisories/GHSA-cf7p-gm2m-833m)
- [cryptography](https://github.com/advisories/GHSA-jm77-qphf-c4w8)
- [GitPython](https://github.com/advisories/GHSA-pr76-5cm5-w9cj)

- Use flake8 instead of flake9 to enable removing transitive override.

- Update dependencies due to vulnerabilities.
- requests: [CVE-2023-32681](https://github.com/advisories/GHSA-j8r2-6x86-q33q)
- starlette: [no CVE](https://github.com/advisories/GHSA-v5gw-mw7f-84px)
- Add timeout to requests calls [CWE-400](https://cwe.mitre.org/data/definitions/400.html)

- Add documentation guidelines enforced with vale.
- Update packages due to vulnerability [CVE-2023-0286](https://github.com/advisories/GHSA-x4qr-2fvf-3mr5) and others.

- Bump GitPython due to vulnerability [CVE-2022-24439](https://github.com/advisories/GHSA-hcpj-qp55-gfph)
- Drop Python 3.6 support due to incompatibility with GitPython > 3.1.29.
- Change method from get to post in testing to fix parameter issue.

- Fix a bug with oidc redirect login