[SDK README - api.video-swift-client] Add summary feature

[bot-api-video]

Changes are for this Asana task.

Summary 😏

• added the new /summaries, /summaries/{summaryId}, and /summaries/{summaryId}/source endpoints with all needed methods
• added the transcriptSummary parameter to POST /videos and PATCH /videos/{videoId}
• defined a new 409 - Conflict error schema with examples - note that the corresponding error page in the documentation will be created in a separate commit on the documentaion repo ℹ️
• added general usage notes in the endpoint descriptions - note that the main "how to use" guide in the documentation will be created in a separate commit on the documentaion repo ℹ️

⚠️ This PR should only be reviewed and should not be merged before release.

Created by @olivierapivideo via apivideo/api.video-api-client-generator#399
Created by @bot-api-video via apivideo/api.video-swift-client#94