## Summary
* Update observation space information and standardise formatting of code blocks in that section
* Remove non-ascii quotation characters
* Update custom blue agent page to match new AgentSession classes.
* Introduce glossary
* Provide a first draft of migration guide for 1.2 to 2.0 (probably not comprehensive)
## Test process
Sphinx is able to build the documentation as checked on my local machine
## Checklist
- [x] This PR is linked to a **work item**
- [x] I have performed **self-review** of the code
- [ ] I have written **tests** for any new functionality added with this PR
- [x] I have updated the **documentation** if this PR changes or adds functionality
- [x] I have run **pre-commit** checks for code style
Related work items: #1602
c61770825a