feat: add support for NetBox v2 API tokens

[MrKeiKun]

Summary

NetBox v2 tokens use Authorization: Bearer nbt_<key>.<token> instead of Authorization: Token <token> (v1). This PR adds auto-detection based on the nbt_ prefix — the same check used by NetBox itself in netbox/api/authentication.py — so no additional provider configuration is needed.

Also corrects the key field validation on netbox_token to cover both token versions: v2 keys are 12 chars, v1 plaintexts are 40 chars.

Token format reference (from NetBox source)

Constant	Value
TOKEN_PREFIX	nbt_ (4 chars)
TOKEN_KEY_LENGTH	12 chars
TOKEN_DEFAULT_LENGTH	40 chars

Full bearer token: nbt_<12-char-key>.<40-char-token> = 57 chars total

Usage

provider "netbox" {
  server_url = "https://netbox.example.com"
  api_token  = "nbt_abc123456789.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"  # v2, auto-detected
}

[fbreckle]

Where did you get the 12 from? I can create tokens with key "123456789" just fine.

[fbreckle]

Imo, just drop this part of the MR and stick to the authentication header part. Then we handle the netbox_token resource in another MR.

[fbreckle]

LGTM and works in my local tests. Run make docs and consider my latest comment, then we're good to go.

[fbreckle]

Imo, just drop this part of the MR and stick to the authentication header part. Then we handle the netbox_token resource in another MR.