[bgp-config] fix create idempotency

[nicolaskagami]

• Adds missing check for description and max_paths fields for idempotency.
• Uses destructuring to exhaustively match on fields so that new ones are less likely to be forgotten.
• Adds a simple smoke test.

Fixes #10765

The BgpConfig create endpoint explicitly checks for idempotency and returns OK if all fields match an already existing entry. Regardless of whether we want to keep this behavior, this PR merely fixes the implementation for a few fields.

[david-crespo]

This looks good if we want to keep the idempotency behavior. I'm investigating (with a prototype I'll post as a draft PR) the alternative of making it work like all the other endpoints and just 409 on a name conflict.

[nicolaskagami]

This looks good if we want to keep the idempotency behavior. I'm investigating (with a prototype I'll post as a draft PR) the alternative of making it work like all the other endpoints and just 409 on a name conflict.

I think it makes sense to fix the idempotency for now while we discuss removing it.