feat: customize getting started page (#5707)

* feat: add getting-started patch

This modifies the text on the Getting Started page to promote
coder/coder.

* feat: add --disable-getting-started-override

This adds a new CLI flag to code-server called
`--disable-getting-started` which will be used in Code to not use
Coder's custom Getting Started text.

* refactor: conditionally show coder getting started

This modifies the getting started patch changes to work with the new
`--disable-getting-started-override`.

The flag is false by default meaning the Coder getting started is shown.
By passing the flag to code-server, it will not be shown.

* docs: update faq for getting started override

* docs: update getting-started patch description

* fixup!: update patch

* fixup!: unit test

* feat: add more tests

* fixup!: use correct env var in tests

Co-authored-by: repo-ranger[bot] <39074581+repo-ranger[bot]@users.noreply.github.com>

docs/FAQ.md

@@ -32,6 +32,7 @@
 - [Does code-server have any security login validation?](#does-code-server-have-any-security-login-validation)
 - [Are there community projects involving code-server?](#are-there-community-projects-involving-code-server)
 - [How do I change the port?](#how-do-i-change-the-port)
+- [How do I hide the coder/coder promotion?](#how-do-i-hide-the-codercoder-promotion)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 <!-- prettier-ignore-end -->
@@ -418,3 +419,7 @@ There are two ways to change the port on which code-server runs:
 
 1. with an environment variable e.g. `PORT=3000 code-server`
 2. using the flag `--bind-addr` e.g. `code-server --bind-addr localhost:3000`
+
+## How do I hide the coder/coder promotion?
+
+You can pass the flag `--disable-getting-started-override` to `code-server`.