Headings and descriptions for API reference

[speller26]

Describe the feature you'd like
The API reference in the documentation website is rather barebones and unintuitive:

1. The table of contents include many unnecessary and nondescript headings, namely the top-level "braket namespace," "Subpackages," and "Submodules," as well every single method and property for each class
2. The modules have no descriptions
3. The table of contents show only module paths instead of easy-to-understand names

It should be updated to be more readable and present more useful information.

How would this feature be used? Please describe.

Improving the readability of the documentation would make it much easier to learn how to use the Braket SDK (in conjunction with the example notebooks).

Requirements

1. Remove all the unnecessary levels in the table of contents.
2. Add a descriptive paragraph to each top-level module
3. Add readable module aliases (e.g. Analog Hamiltonian Simulation for "braket.ahs package"); for modules that are class files (e.g. AwsDevice), this can literally be just the class name.