feat: Make seek bar keyboard skip increment configurable (#8919)

## Description
Pressing the arrow and page keys seeks, currently by a set interval.
This change makes this configurable.

## Specific Changes proposed
Adds options that can be included in player options which set the
increments to used.
```
{
  controlBar: {
    progressControl: {
      seekBar: {
        stepSeconds: 2,
        pageMultiplier: 4
      }
    }
  }
}
```
Defaults remain as 5 seconds for left/right and 12x multiplier for page
up/down.

## Requirements Checklist
- [x] Feature implemented / Bug fixed
- [ ] If necessary, more likely in a feature request than a bug fix
- [x] Change has been verified in an actual browser (Chrome, Firefox,
IE)
  - [x] Unit Tests updated or fixed
  - [ ] Docs/guides updated
- [ ] Example created ([starter template on
JSBin](https://codepen.io/gkatsev/pen/GwZegv?editors=1000#0))
- [x] Has no DOM changes which impact accessiblilty or trigger warnings
(e.g. Chrome issues tab)
  - [x] Has no changes to JSDoc which cause `npm run docs:api` to error
- [ ] Reviewed by Two Core Contributors