Add a dodal glossary and style guide

[dperl-dls]

There are some things which we have discussed which are not easily enforceable through linting, we should add a document about best practices, e.g.

• how to use the new Reference to add private references to other devices or signals
• naming devices and their associated enums
  • enums that live in a device file don't need to include the device name
  • composite devices which exist to expose a synthetic signal should be named after that synthetic signal and not the component devices