Added Summaries to API Models & Added ContentClassificiationLabel API Endpoint

[koishibuh]

Added summaries to the following API models: Ads, GetCheermotes, CreateClips, & GetClips

[koishibuh]

• Updated several models to have summaries

• With Twitch releasing the new Content Classification Labels, several models needed to be updated: GetChannelInformation (TwitchDocs) & ModifyChannelInformation (TwitchDocs) to include the new properties.

• Created a ContentClassificationLabel Enum with the values that Twitch expects for the Content Classification Labels.

• TODO: Sorry, should have double checked this, but there is also a new end point called GetContentClassificationLabels (TwitchDocs) that will need to be added. I will attempt to add this tomorrow and try not to break anything. (This should have also been a separate PR my bad)

[koishibuh]

Twitch released a new endpoint GetContentClassificationLabels (TwitchDocs) that returns the list of Content Classification Labels so I:

• Added ContentClassificationLabel to the Api.Helix.Helix class
• Added ContentClassificationLabels class to Api.Helix with GetContentClassificationAsync method
• Added GetContentClassificationLabelsResponse with model to Api.Helix.Models.ContentClassificationLabels

Not sure if there is anything other place I was supposed to add things to as I just followed the other classes as an example. I also haven't tested this to make sure it actually works since I don't know how to do that properly.

[koishibuh]

• Updated summaries for Ad & Analytics in Api.Helix to include links to Twitch API Documents
• Found a bug in the summary for Analytics.GetExtensionAnalyticsAsync() that looks like was a copy-paste error from GetGameAnalytics which had different Started_At & Ended_at information. Updated to correct information.
• Added missing Pagination property in GetExtensionAnalyticsResponse