Fixes #792

An initial migration of the existing specs as of
[`e59efd63a2165866584833e91e1cb8a6ed8c8203`](https://github.com/celestiaorg/celestia-specs/tree/e59efd63a2165866584833e91e1cb8a6ed8c8203).
It's expected that there are a few broken links and extra content that
has to be pruned, along with incorrect content. The important thing is
to not miss anything.

Also sets up a CI workflow that will build the book.

See
https://github.com/celestiaorg/celestia-app/actions/runs/3136139613/jobs/5092673489

Run [Markdown Table
Prettifier](https://github.com/darkriszty/MarkdownTablePrettify-VSCodeExt).

Ref:
#793 (comment)
by @rootulp

Closes #807

Closes #728

Closes #729


[Rendered](https://github.com/celestiaorg/celestia-app/blob/e6f00791df41a4257b677df52747e6453856770e/specs/src/specs/data_structures.md#share)

Co-authored-by: John Adler <[email protected]>

Closes #883

Co-authored-by: CHAMI Rachid <[email protected]>

Part of #1153

Should only be merged if
#1181 is merged

Closes #1120

Co-authored-by: John Adler <[email protected]>

Closes #1151

Co-authored-by: John Adler <[email protected]>

Closes #1247

Closes #1175 

See the implementation
[here](https://github.com/celestiaorg/celestia-app/blob/d7ac0b84765db3f649cd82326e3ead066d164637/pkg/shares/tail_padding.go#L9-L21).

## Screenshot

<img width="891" alt="Screenshot 2023-01-17 at 11 04 14 AM"
src="https://user-images.githubusercontent.com/3699047/212949826-4b213925-91f0-4653-b375-545c89c17acc.png">

Context: #1353
Closes #1344

## Screenshot

<img width="746" alt="Screenshot 2023-02-08 at 11 55 07 AM"
src="https://user-images.githubusercontent.com/3699047/217598202-15737680-d81b-4771-9940-75aa1830eaa2.png">

…#1420)

This aims to clarify that the minimum square size in non-interactive
default rules should be a power of 2. For example, for a message of
length 23, the minimum square size is `8*8` (but not `5*5`). (based on a
discussion in Slack)

- [x] NA ~~New and updated code has appropriate documentation~~
- [x] NA ~~New and updated code has new and/or updated testing~~
- [x] Required CI checks are passing
- [x] NA ~~Visual proof for any user facing features like CLI or
documentation updates~~
- [x] NA ~~Linked issues closed with keywords~~

## Motivation 
The table of contents at the top of each file can be a maintenance
burden. We can auto-generate it with
[mdbook-toc](https://github.com/badboy/mdbook-toc).

## Screenshot

Before | After
--- | ---
<img width="500" alt="before"
src="https://user-images.githubusercontent.com/3699047/222535783-8ad53ec3-43db-4e4b-ad8f-ea974061190b.png">
| <img width="479" alt="after"
src="https://user-images.githubusercontent.com/3699047/222535796-39c4172d-79b9-4e64-a492-7a68c37f5381.png">

Running make lint locally doesn't catch these errors

Co-authored-by: Matthew Sevey <[email protected]>