Match framerate in DefaultVideoFrameProcessorPipeline with input stream

[shi-su]

Issue #:

Description of changes:
In DefaultVideoFrameProcessorPipeline the framerate is set as 15 fps. As a result, once video frame processor is applied, video framerate will be capped at 15 fps even if input fps is higher. This change matches this framerate with input video stream.

Testing:
Smoke tested and verified video fps matches input stream after applying a video filter.

Can these tested using a demo application? Please provide reproducible step-by-step instructions.

1. Start a call and add an attendee with 30 fps video;
2. Start video and verify video framerate is 30 fps;
3. Apply background background blur and verify video framerate is still 30 fps (actual framerate may be about 3 fps lower due to video frame processing).

Checklist:

1. Have you successfully run npm run build:release locally?
   y

2. Do you add, modify, or delete public API definitions? If yes, has that been reviewed and approved?
   n

3. Do you change the wire protocol, e.g. the request method? If yes, has that been reviewed and approved?
   n

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.