Grafana-django-saml2-auth

In this minor release, PKI support for JWT token encoding/decoding is added 24. As part of the same PR, documentation (readme and authors) are converted to markdown, cleaned up, and updated with a detailed table describing each configuration setting. A new section is also added that explains [JWT signing algorithm and settings](https://github.com/grafana/django-saml2-auth#jwt-signing-algorithm-and-settings).

This release includes updates to 2 dependencies (22):

- `pysaml2` to `7.1.0`
- `PyJWT` to `2.3.0`.

As the issue is raised in 20, I created a PR 23 and introduced `REQUIRE_TOKEN` settings (default: `True`) to make `token` field optional in the attribute statement.

Since the last release, [v3.0.0](https://github.com/grafana/django-saml2-auth/releases/tag/3.0.0), there has been some minor issues fixed and enhancements added by jean-sh and syre and me. I just tagged this to differentiate from further changes that might happen down the line, like dependency updates and such.

This release includes lots of changes: **71** commits, **92** lines of commit messages and **3** reviewers (thanks to Griatch, Menda and esquonk). This release is backward incompatible and includes refactoring, improving code readability (docstrings, annotations, ...), tests, new shiny features and the like. It started as a task to refactor the code, but ended with many other things.

The biggest change so far was adding tests along with GitHub Actions as CI and the introduction of SP-initiated SSO. The exception and error handling is also greatly improved. For a more detailed description of what happened in this release, please read the [changelog](https://github.com/loadimpact/django-saml2-auth/pull/14).