feat(farmer-app): audio support

[chrismclarke]

Is your feature request related to a problem? Please describe.
The content team is planning to provide audio prompts to help make certain pages within the app more accessible. These should be made available through the app.

Describe the solution you'd like
Create a shared audio-playback component and service to handle playing of audio snippets. The component should show a UI button as seen in Figma Mockups, which when pressed plays the audio.

It might also be nice to change the UI if audio is playing, to allow the user to pause the audio. Additionally a shared service will likely be required to track globally any audio playing, and be able to pause existing audio either when the user starts new audio playback or navigates off screen (can likely use component OnDestroy to stop playback but will need global service to stop any other audio triggered elsewhere)

Additional context

• Likely will need to add a placeholder audio asset for testing purposes. In the future these will come from the database
• It should be possible to play audio programatically (without rendering an <audio> element tag), see examples in https://developer.mozilla.org/en-US/docs/Web/API/HTMLAudioElement#basic_usage
• In the future it would be good to integrate audio with the existing tour system, however likely that should be saved for follow-up PR