Support additional format of field mask in query parameters

[johanstokking]

Summary:

At the moment there are two formats to pass the field mask for get requests:

1. ?field_mask.paths=field1&field_mask.paths=field2
2. ?field_mask.paths[]=field1&field_mask.paths[]=field2

It might be convenient to introduce the comma-separated version:
?field_mask.paths=field1,field2

Why do we need this?

• Short and readable endpoints.
• The process of constructing the url becomes easier

What is already there? What do you see now?

All parameters in the comma-separated format are stored as a single value in the FieldMask.Paths slice.

What is missing? What do you want to see?

Thread every comma-separated field name individually

How do you propose to implement this?

What can you do yourself and what do you need help with?

File the feature request

@htdvisser please fill the milestone

---

Original issue: https://github.com/TheThingsIndustries/lorawan-stack/issues/1564 by @bafonins

[kschiffer]

From what I see, this issue is resolved, or there is a third option that we overlooked that serves our needs perfectly.
Following formats are possible:

• ?field_mask.paths=field1&field_mask.paths=field2
• ?field_mask.paths[]=field1&field_mask.paths[]=field2
• ?field_mask=field1,field2, easily the most convenient

Tested in the IS device registry.

[htdvisser]

That third option is indeed the best. Seems to be supported by grpc-gateway since grpc-ecosystem/grpc-gateway#529. Not sure why it wasn't working before.