Add Partytown support

[ijkml]

While the Umami script is lightweight (about 2kb), the execution might be costly. Adding the script to a production website seemed to significantly affect the lighthouse scores (further testing needed).

Even if this cost is small/average, support for Partytown would still likely help some.

To implement Partytown, I could either:

• bundle Partytown as a dependency (for all),
• allow specifying whether or not to use Partytown in config (opt-in),
• or... (leave as is).