Move from gitbook to docusaurus, build docs in Travis CI (#10970)

* fix: ignore unknown fields in more RPC responses

* Remove mdbook infrastructure

* Delete gitattributes and other theme related items

Move all docs to /docs folder to support Docusaurus

* all docs need to be moved to /docs

* can be changed in the future

Add Docusaurus infrastructure

* initialize docusaurus repo

Remove trailing whitespace, add support for eslint

Change Docusaurus configuration to support `src`

* No need to rename the folder! Change a setting and we're all good to
go.

* Fixing rebase items

* Remove unneccessary markdown file, fix type

* Some fonts are hard to read. Others, not so much. Rubik, you've been
sidelined. Roboto, into the limelight!

* As much as we all love tutorials, I think we all can navigate around a
markdown file. Say goodbye, `mdx.md`.

* Setup deployment infrastructure

* Move docs job from buildkite to travic

* Fix travis config

* Add vercel token to travis config

* Only deploy docs after merge

* Docker rust env

* Revert "Docker rust env"

This reverts commit f84bc208e807aab1c0d97c7588bbfada1fedfa7c.

* Build CLI usage from docker

* Pacify shellcheck

* Run job on PR and new commits for publication

* Update README

* Fix svg image building

* shellcheck

Co-authored-by: Michael Vines <mvines@gmail.com>
Co-authored-by: Ryan Shea <rmshea@users.noreply.github.com>
Co-authored-by: publish-docs.sh <maintainers@solana.com>

docs/README.md

@@ -1,31 +1,38 @@
-Building the Solana Docs
----
+# Docs Readme
 
-Install dependencies, build, and test the docs:
+Solana's Docs are built using [Docusaurus 2](https://v2.docusaurus.io/) with `npm`.
+Static content delivery is handled using `vercel`.
 
-```bash
-$ brew install coreutils
-$ brew install mscgen
-$ cargo install svgbob_cli
-$ cargo install mdbook-linkcheck
-$ cargo install mdbook
-$ ./build.sh
+### Installation
+
+```
+$ npm install
 ```
 
-Run any Rust tests in the markdown:
+### Local Development
 
-```bash
-$ make test
+```
+$ npm run start
 ```
 
-Render markdown as HTML:
+This command starts a local development server and open up a browser window. Most changes are reflected live without having to restart the server.
 
-```bash
-$ make build
+### Build
+#### Local Build Testing
+```
+$ npm run build
 ```
 
-Render and view the docs:
+This command generates static content into the `build` directory and can be
+served using any static contents hosting service.
 
-```bash
-$ make open
-```
+#### CI Build Flow
+The docs are built and published in Travis CI with the `docs/build.sh` script.
+On each PR, the docs are built, but not published.
+
+In each post-commit build, docs are built and published using `vercel` to their
+respective domain depending on the build branch.
+
+ - Master branch docs are published to `edge.docs.solana.com`
+ - Beta branch docs are published to `beta.docs.solana.com`
+ - Latest release tag docs are published to `docs.solana.com`