223 metadata injector

[jr1221]

Changes

Adds a metadata injector. It basically splits off socket functionality from mqtt_processor into its own file, and hides the metadata behind a flag.

Notes

• Currently only viewer count implmented metadata type

To Do

Any remaining things that need to get done

• Figure out what to do about latency sender
• Improve structure of sending code to avoid code duplication
• Actually add senders for timers (More sustainable way to store timer values (for charging screen timers) #207)
• Improve/figure out sending something other than clientdata.

Checklist

• No merge conflicts
• All checks passing
• Screenshots of UI changes (see Screenshots section)
• Remove any non-applicable sections of this template
• Assign the PR to yourself
• No package-lock.json changes (unless dependencies have changed)
• Request reviewers & ping on Slack
• PR is linked to the ticket (fill in the closes line below)

Closes #223