Add WC tracking mu-plugin on new site creation

[NickGreen]

Add WC tracking mu-plugin on new site creation

mu-plugin link: https://github.com/a8cteam51/wc-usage-tracking-auto-opt-in

Slack reference: https://a8c.slack.com/archives/C01M1J49Q75/p1659460668510099?thread_ts=1659371343.021599&cid=C01M1J49Q75

[georgestephanis]

Do we want this on every new site, even if they're not using woocommerce?

Prior art I'm pushing through now here on how to do this:

#115

[NickGreen]

Do we want this on every new site, even if they're not using woocommerce?

It now includes a Sensei snippet, too.

But regardless, I can't think of a way to tell if they are planning on adding Woo or Sensei later on after creating a new site, so it seems like we might just have to add it to every one.

[georgestephanis]

That PR should address this, and serve as a proof of concept for any further submodules we'd like to add.