Init docs for snap-in configuration

Author: codeon

fern/docs/pages/references/snap-in-configuration.mdx

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+## Snap-in configuration
+
+Snap-ins have keyrings and inputs that can be set from the UI by going to the snap-in configuration page. The snap-in configuration page will list all the keyrings and inputs which can then be set by the user installing the snap-in. 
+In some instances, the default rendering page is not easy to use or doesn't faciliate the user's needs. 
+In such cases, the snap-in configuration page can be defined by the snap-in developer. The snap-in developer can define a snap-in function that can be used to generate a snap-kit which renders input elements as well as other elements to make the page easier to configure or pull in data from other systems as well. 
+For example, if the developers needs to ask the user for a Slack channel, they may need to get the list of channels from their Slack workspace, show the channel names in the drop down and when the user selects a channel, the snap-kit can pass back the channel ID as that is what is used in the APIs.
+This enables a lot of flexibility in the snap-in configuration page making it easier to configure snap-ins and giving developers more control of how users interact with their snap-ins.
+
+## How to define a snap-in configuration page
+In your manifest, add the following section to enable a configuration_handler:
+
+```yaml
+functions:
+  - name: org_snap_in_configuration_handler
+    description: Handler for processing organization configuration options.
+  - name: user_snap_in_configuration_handler
+    description: Handler for processing user configuration options.
+  - name: config_initializer
+    description: Generates the initial configuration options for both organization and user.
+
+configuration_handler:
+ organization:
+    initializer: config_initializer
+    snap_kit_action_name: org_snap_in_configuration_handler
+
+  user:
+    initializer: config_initializer
+    snap_kit_action_name: user_snap_in_configuration_handler
+```
+
+The above YAML segment creates three functions and connects them to the configuration_handler to enable custom snap-kits to be rendered as the snap-in configuration page. The `config_initializer` function is used to generate the initial configuration options for both organization and user. The `org_snap_in_configuration_handler` and `user_snap_in_configuration_handler` functions are used to process the organization and user configuration options respectively.
+
+When the snap-in configuration page is loaded, the snap-in will call the `config_initializer` function to get the initial configuration options. Further actions on the returned snap-kit will then call the `org_snap_in_configuration_handler` or `user_snap_in_configuration_handler` function to render the snap-kit for the organization or user respectively.
+
+The functions should always return a valid snap-kit JSON.