fix(lb): frontend inherit zone from related lb

[m-matth]

a Terraform script with default zone different from Lb one, will fail to create the Lb frontend on the correct zone, leading to a error 400.

This PR set the frontend resource zone according to the related lb. Also add some zone related check.

[codecov-commenter]

Codecov Report

Merging #1671 (9f25f4e) into master (4d4491d) will decrease coverage by 0.03%.
The diff coverage is 21.05%.

@@            Coverage Diff             @@
##           master    #1671      +/-   ##
==========================================
- Coverage   73.67%   73.64%   -0.04%     
==========================================
  Files         145      145              
  Lines       23627    23645      +18     
==========================================
+ Hits        17407    17413       +6     
- Misses       4695     4703       +8     
- Partials     1525     1529       +4     

Impacted Files	Coverage Δ
scaleway/resource_lb.go	69.02% <14.28%> (-1.07%)	⬇️
scaleway/resource_lb_frontend.go	76.77% <25.00%> (-1.62%)	⬇️
scaleway/retryable_transport.go	73.21% <0.00%> (+5.35%)	⬆️

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[Codelax]

Hi thanks for your contribution.

The issue with zoned and regional IDs is that we cannot enforce usage of this format.
The following snippets should work:

resource "scaleway_lb_ip" "main" {
  zone = "fr-par-1"
}

resource "scaleway_lb" "base" {
  ip_id  = scaleway_lb_ip.main.id
  zone   = scaleway_lb_ip.main.zone
  type   = "LB-S"
}

and

resource "scaleway_lb" "base" {
  ip_id  = "xxxx-xxxx-xxxx-xxxx"
  type   = "LB-S"
}

User is able to use a locality ID aswell as a bare ID.
Also, as we can see in lb documentation basic's example (which is the first snippet before), the recommended way is to pass down locality from one resource to another if you want to guarantee they are in the same one.

This is still a great issue that you have highlighted, we should provide more errors when validating a config.

[m-matth]

i see, then it needs to add a zone parameter to every lb ressource as it misse for frontend, backend and route. (as well as as some other param like project_id maybe).

The associated use case is creating one lb on each zone.

[Codelax]

Ok, thanks for this, I will make a pass on it.
It should be ok in the next release, sorry for the inconvenience.