docs: fix access token config to show correct nested JSON structure (#1741)

Author: gabtorre

docs/cli/how-tos/managing-access-tokens.mdx

@@ -1,23 +1,35 @@
 # Managing access tokens
 
-The `auth.accessTokens` setting in Sourcegraph's site configuration allows admins to fine-tune parameters related to access tokens.
+The `auth.accessTokens` setting in Sourcegraph's site configuration allows admins to fine-tune parameters related to access tokens:
+
+```json
+{
+  "auth.accessTokens": {
+    "allow": "all-users-create",
+    "allowNoExpiration": false,
+    "maxTokensPerUser": 25,
+    "expirationOptionDays": [7, 14, 30, 60, 90],
+    "defaultExpirationDays": 90
+  }
+}
+```
 
 ## Access token creation
 
-The `auth.accessTokens.allow` configuration field permits or restricts the creation of access tokens. It can be assigned one of three values: "none," "all-users-create" (which is the default option), or "site-admin-create.”
+The `allow` property permits or restricts the use of access tokens. It can be assigned one of three values:
 
--   `none` Disables the creation of access tokens.
--   `all-users-create` Allows users to create their own token.
--   `site-admin-create` Allows site admins to create tokens for users.
+-   `all-users-create` (default) Enables all users to create access tokens.
+-   `site-admin-create` Restricts creation of new tokens to admin users (existing tokens will still work until revoked).
+-   `none` Disables access tokens entirely.
 
-`auth.accessTokens.maxTokensPerUser` - This config field determines the maximum number of active access tokens a user can have. The default maximum is 25 tokens.
+The `maxTokensPerUser` property determines the maximum number of active access tokens a user can have. The default maximum is 25 tokens.
 
 ## Access token expiration
 
 Admins can set expiration policies for access tokens. After this specified period, tokens will automatically lose their access. Note that tokens created before version 5.3 do not expire; this policy only applies to **new** tokens.
 
-`auth.accessTokens.allowNoExpiration` - This controls whether tokens can be created with no expiration date. The default setting is false.
+`allowNoExpiration` - Controls whether tokens can be created with no expiration date. The default setting is false.
 
-`auth.accessTokens.expirationOptionDays` - This represents the options users are presented with for the token expiration period. The default options are [7, 14, 30, 60, 90].
+`expirationOptionDays` - The options users are presented with for the token expiration period. The default options are [7, 14, 30, 60, 90].
 
-`auth.accessTokens.defaultExpirationDays` - This sets the default duration selection when creating a new access token. The default is 90 days.
+`defaultExpirationDays` - The default duration selection when creating a new access token. The default is 90 days.