docs: Add syntax highlighting languages to code blocks.

Signed-off-by: Anders Kaseorg <anders@zulip.com>
(cherry picked from commit b29b6f6526)

docs/documentation/api.md

@@ -101,7 +101,7 @@ defined using a special Markdown extension
 (`zerver/openapi/markdown_extension.py`).  To use this extension, one
 writes a Markdown file block that looks something like this:
 
-```
+```md
 {start_tabs}
 {tab|python}
 
@@ -169,7 +169,7 @@ an API endpoint supports.  You'll see this in files like
 directive (implemented in
 `zerver/lib/markdown/api_arguments_table_generator.py`):
 
-```
+```md
 {generate_api_arguments_table|zulip.yaml|/messages/render:post}
 ```
 
@@ -186,7 +186,7 @@ You can use the following Markdown directive to render the fixtures
 defined in the OpenAPI `zulip.yaml` for a given endpoint and status
 code:
 
-```
+```md
 {generate_code_example|/messages/render:post|fixture(200)}
 ```
 

docs/documentation/integrations.md

@@ -46,7 +46,7 @@ Usually, this involves a few steps:
   If your new integration is an incoming webhook integration, you can generate
   the screenshot using `tools/generate-integration-docs-screenshot`:
 
-  ```sh
+  ```bash
   ./tools/generate-integration-docs-screenshot --integration integrationname
   ```
 
@@ -136,7 +136,7 @@ Here are a few common macros used to document Zulip's integrations:
 * `{!webhook-url-with-bot-email.md!}` - Used in certain non-webhook integrations
   to generate URLs of the form:
 
-    ```
+    ```text
     https://bot_email:bot_api_key@yourZulipDomain.zulipchat.com/api/v1/external/beanstalk
     ```
 

docs/documentation/openapi.md

@@ -40,7 +40,7 @@ types of authentication, and configure other settings. Once defined,
 information in this section rarely changes.
 
 For example, the `swagger` and `info` objects look like this:
-```
+```yaml
 # Basic Swagger UI info
 openapi: 3.0.1
 info:
@@ -79,7 +79,7 @@ expects a GET request with one
 Basic authentication, and returns a JSON response containing `msg`,
 `result`, and `presence` values.
 
-```
+```yaml
 /users/{user}/presence:
   get:
     description: Get presence data for another user.
@@ -119,7 +119,7 @@ contains schemas referenced by other objects. For example,
 contains three required parameters.  Two are strings, and one is an
 integer.
 
-```
+```yaml
 MessageResponse:
   type: object
   required:
@@ -183,7 +183,7 @@ correct.
 
 ### Examples:
 
-```
+```yaml
 Description: |
              This description has multiple lines.
              Sometimes descriptions can go on for

docs/documentation/overview.md

@@ -43,7 +43,7 @@ your changes), the dependencies are automatically installed as part of
 Zulip development environment provisioning, and you can build the
 documentation using:
 
-```
+```bash
 ./tools/build-docs
 ```
 

docs/documentation/user.md

@@ -210,7 +210,7 @@ instructions. For instance, it may address a common problem users may
 encounter while following the instructions, or point to an option for power
 users.
 
-```
+```md
 !!! tip ""
     If you've forgotten your password, see the
     [Change your password](/help/change-your-password) page for
@@ -220,7 +220,7 @@ users.
 A **warning** is a note on what happens when there is some kind of problem.
 Tips are more common than warnings.
 
-```
+```md
 !!! warn ""
     **Note:** If you attempt to input a nonexistent stream name, an error
     message will appear.
@@ -237,14 +237,16 @@ design to easily show the instructions for different
 [platforms](https://zulip.com/help/logging-out) in user docs,
 languages in API docs, etc.  To create a tab switcher, write:
 
-    {start_tabs}
-    {tab|desktop-web}
-    # First tab's content
-    {tab|ios}
-    # Second tab's content
-    {tab|android}
-    # Third tab's content
-    {end_tabs}
+```md
+{start_tabs}
+{tab|desktop-web}
+# First tab's content
+{tab|ios}
+# Second tab's content
+{tab|android}
+# Third tab's content
+{end_tabs}
+```
 
 The tab identifiers (e.g. `desktop-web` above) and their mappings to
 the tabs' labels are declared in