I looked into it on behalf of a friend who wanted to join me, but has back issues. I have good and bad news:
1. Yes there are services
2. Cost is higher, and there was often a 2-bag minimum
3. You need to submit your route ahead of time
4. “Pilgrim accommodations” won’t accept dropped bags, so you’ll need fo use traditional hotels, b&bs, etc
My friend opted out, so I won’t be using a baggage transport service, so I can’t vouch for how they work in the end.