Storyteller - add playhead functionality for animated video

[jsavella]

Please always provide the GitHub issue(s) your PR is for, as well as test URLs where your change can be observed (before and after):

Fix #104

Test URLs:

• Original: https://www.esri.com/en-us/about/about-esri/overview
• Before: https://main--esri--aemsites.hlx.live/
• After: https://storyteller-playbutton--esri--aemsites.hlx.live/

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Commits

* [a884000](https://github.com/aemsites/esri/commit/a88400035f676c6acc6aaa169b0f3382e2003e8d) :white_check_mark: (latest) * [dffe298](https://github.com/aemsites/esri/commit/dffe29806aa26a045b1e5b1bf58c0cff7b6789dd) :white_check_mark: * [572e4f4](https://github.com/aemsites/esri/commit/572e4f44c532528cc7805ea779424451ba1b6d64) :white_check_mark: * [cb30f0e](https://github.com/aemsites/esri/commit/cb30f0ecd76c9457a76316b783681cba1ceeb68d) :white_check_mark: * [8913334](https://github.com/aemsites/esri/commit/8913334a5d3fcfd0f1453488ce2623d26d7e00f8) :white_check_mark: * [9790324](https://github.com/aemsites/esri/commit/9790324d8fb68c63737b95f7831802fe04d509d8) :white_check_mark: * [fb52903](https://github.com/aemsites/esri/commit/fb5290344642ba9a2616f9be85732efc656ff00a) :white_check_mark: * [125dded](https://github.com/aemsites/esri/commit/125ddede23d2c484606a27c9cec19c4d893e7766) :white_check_mark: * [7c9dc00](https://github.com/aemsites/esri/commit/7c9dc00601e43ccbfdf455b1cf0c232ae8778fbf) :white_check_mark: * [5e5e33e](https://github.com/aemsites/esri/commit/5e5e33ee4e0e9fdc57c89412d06fca71dbf11627) :white_check_mark: * [84a2373](https://github.com/aemsites/esri/commit/84a2373cf3b6db9a8053620345b1558f44522128) :white_check_mark: * [059f2eb](https://github.com/aemsites/esri/commit/059f2eb89864eacc7d7a065a0d8a5b40a63bda12) :white_check_mark: * [1d5141f](https://github.com/aemsites/esri/commit/1d5141fa3eecd7133cf0a745abe8d67ba4d993fd) :white_check_mark: * [e899e28](https://github.com/aemsites/esri/commit/e899e283fac6209ff37c73149d9167ea268dce90) :white_check_mark: * [f631f56](https://github.com/aemsites/esri/commit/f631f5699e9b92bed9efa0d47d1cc78953212508) :white_check_mark: * [5f0d956](https://github.com/aemsites/esri/commit/5f0d956085977a70830c91cf028f97f1ed4824f5) :white_check_mark: * [61c419e](https://github.com/aemsites/esri/commit/61c419e135e7aba0267917b51dedfdfd979a390c) :white_check_mark: * [53edbd8](https://github.com/aemsites/esri/commit/53edbd8a15b218c82b4e8217913ee98220613473) :white_check_mark:

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