fix: res def secret refs with null values

[johanneswuerbach]

When using an explicit type like:

object({
    ref     = optional(string)
    store   = optional(string)
    value   = optional(string)
    version = optional(string)
})

to pass around secret references, terraform will serialise optional values to null.

This null values causes the provider to break:

│ Error: Provider produced inconsistent result after apply
│
│ When applying changes to module.base.module.config_imagepullsecret.humanitec_resource_definition.main, provider "provider[\"registry.terraform.io/humanitec/humanitec\"]" produced an unexpected new value: .driver_inputs.secret_refs: was
│ cty.StringVal("{\"AWS_ACCESS_KEY_ID\":{\"ref\":\"XYZ\",\"store\":\"XYZ\",\"value\":null,\"version\":\"terraform-20240607165723165200000005\"}}"),
│ but now
│ cty.StringVal("{\"AWS_ACCESS_KEY_ID\":{\"ref\":\"XYZ\",\"store\":\"XYZ\",\"version\":\"terraform-20240607165723165200000005\"}}").

Instead of generally taking the API response, change the logic to merge the API response and the local state.

[delca85]

LGTM (and thanks).
I could not find any test with nested secret references (I saw TestMergeResourceDefinitionSecretRefResponse but I mean e2e tests) and it might make sense to have one.

[mateuszjenek]

👍