77 feature request support for returning pause ads

[AxelHolst]

Add Support for Pause Ads

This PR implements a new feature to support Pause Ads in the test-adserver. It adds a new endpoint /pause-ad that returns a VAST XML response suitable for pause ads.

Changes

• Added a new /pause-ad endpoint that generates and returns a VAST XML for pause ads
• Implemented PauseAdVastBuilder to create VAST XML specifically for pause ads
• Updated the Session class to handle pause ad requests
• Added a new response format PAUSE_AD to constants

Testing

The VAST XML generated has been tested with the Video Suite Inspector (https://googleads.github.io/googleads-ima-html5/vsi/).

Observations:

• The image is visible, but only a cropped part of it is shown.
• The image is displayed continuously, regardless of whether the video is paused or not.

Questions:

1. Is it correct that the pause logic cannot be implemented in the XML and must be handled by the video player's logic?
2. Are there other ways to test if a pausing functionality could work with this XML?
3. What might be causing only a cropped part of the image to be visible, and how can we address this? (Fixed)

Notes

• The pause ad is implemented as a non-linear ad with a static image resource.
• Users can specify the parameters User ID, Vast version, width and height for the pause ad image. (Thoughts?)
• The VAST response includes tracking events for start, complete, and pause, which can be used by compatible video players.