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>

ci/buildkite-pipeline.sh

@@ -211,12 +211,7 @@ pull_or_push_steps() {
     all_test_steps
   fi
 
-  # doc/ changes:
-  if affects ^docs/; then
-    command_step docs ". ci/rust-version.sh; ci/docker-run.sh \$\$rust_nightly_docker_image docs/build.sh" 5
-  fi
-
-  # web3.js and explorer changes run on Travis...
+  # web3.js, explorer and docs changes run on Travis...
 }