feat: add metadata and cardMetadata to ios docs (#32)

docs/sdks/mobile/ios/events.mdx

@@ -56,3 +56,25 @@ myTextField.subject.sink { completion in
     ...
 }.store(in: &cancellables)
 ```
+
+## Using Metadata for Event Values
+
+Instead of subscribing to events, the same properties can be accessed at any time from the `metadata` property on all elements.
+
+Additionally, the card related event [details](#elementeventdetail-types) can be accessed from the `cardMetadata` property only on [`CardNumberUITextField`](/docs/sdks/mobile/ios/types#cardnumberuitextfield).
+
+The following are the available properties accessible from `metadata`.
+
+| Property      | Type   | Description                                                                                                |
+| ------------- |--------|------------------------------------------------------------------------------------------------------------|
+| complete      | _Bool_ | Whether the input `valid` and `maskSatisfied` properties are `true`.                                       |
+| valid         | _Bool_ | Whether the input is `valid` according to `validation` for each element.                                   |
+| maskSatisfied | _Bool_ | Whether the input satisfies the `mask` length requirements.                                                |
+
+The following are the available properties accessible from `cardMetadata`.
+
+| Property | Type | Description |
+| --- | --- | --- |
+| cardBrand | _String_ | [Card brand](/docs/sdks/mobile/ios/types#card-brands) name when a card number can be identified. |
+| cardLast4 | _String_ | Last 4 digits of a card number when the input is considered `complete`. |
+| cardBin   | _String_ | First 6 digits of a card number when the input is considered `complete`. |

docs/sdks/mobile/ios/index.mdx

@@ -117,3 +117,5 @@ myTextElement.backgroundColor = UIColor( red: 240/255, green: 240/255, blue: 240
 | setValue | A function that recieves an `ElementValueReference` parameter to set the value of the element. Note: `ElementValueReference` instances can only be retrieved from [proxy](/docs/sdks/mobile/ios/services#proxy) responses. |
 | setValueRef | Binds the provided element instance as a value source for the calling element, keeping the value of the calling element in sync with any changes made to the provided element. This makes the caller element read-only. Any iOS element type can be provided as an instance into this function. |
 | setConfig | A function that allows you to set a [mask](/docs/sdks/mobile/ios/options#mask) and [transform](/docs/sdks/mobile/ios/options#transform) on [TextElementUITextField's](/docs/sdks/mobile/ios/types#textelementuitextfield), and [associate a CardNumberUITextField to a CardVerificationCodeUITextField](/docs/sdks/mobile/ios/types#associating-a-cardnumberuitextfield). |
+| metadata  | An object that contains [metadata](/docs/sdks/mobile/ios/events#using-metadata-for-event-values) about the element state in regards to its value.
+| cardMetadata | An object that contains metadata about the card number for the [`CardNumberUITextField`](/docs/sdks/mobile/ios/types#cardnumberuitextfield) element type only.