feat: add open in coder docs, fix missing templates (#4124)

* docs: add open in coder

This adds new documentation for the "Open in Coder" button that admins
can use to get their developers up and running faster.

* fix: display error if template not found

Previously, we weren't handling a case where we tried to get a template
that returned a 404 from the backend.

Now we handle that case in our state machine and display the error
message from the API on the frontend.

* feat: support template query param in index

This adds support to navigate directly to a template from the index by
using the `?template=<name>` query  param.

* Revert "feat: support template query param in index"

This reverts commit bad7ffb677.

We decided to use the `/template/path` route instead.

* fixup!: docs: add open in coder

* docs: add open in coder to dogfood readme

* Update docs/admin/open-in-coder.md

Co-authored-by: Ben Potter <ben@coder.com>

* Update docs/admin/open-in-coder.md

Co-authored-by: Ben Potter <ben@coder.com>

* Update docs/admin/open-in-coder.md

Co-authored-by: Ben Potter <ben@coder.com>

docs/admin/open-in-coder.md

@@ -0,0 +1,27 @@
+# Open in Coder Button
+
+Add a Markdown button to your project's `README.md` to get your developers up and running with Coder with a few clicks.
+
+A basic example looks like this:
+
+```markdown
+[![Open in Coder](https://cdn.coder.com/embed-button.svg)](https://<deployment-url>/templates/<template-name>)
+```
+
+which renders like this:
+
+![Open in Coder](https://cdn.coder.com/embed-button.svg)
+
+You can customize this to take developers directly to your team's template. Read on to learn more.
+
+### Customization
+
+The underlying link for this button consists of the following pieces:
+- <deployment-url>: where your Coder deployment lives i.e. https://dev.coder.com
+- <template-name>: name of template i.e. coder
+
+### template name
+
+A template to redirect your developers to after they authenticate on your deployment.
+
+Example: https://dev.coder.com/templates/coder

docs/manifest.json

@@ -188,6 +188,11 @@
           "title": "Enterprise",
           "description": "Learn how to enable Enterprise features.",
           "path": "./admin/enterprise.md"
+        },
+        {
+          "title": "Open in Coder Button",
+          "description": "Learn how to create an 'Open in Coder' button.",
+          "path": "./admin/open-in-coder.md"
         }
       ]
     },