fix: Corrects errors when plan contains no pricing changes

[mkubilus]

Description

Motivation and Context

This PR fixes a bug where if a plan would result in no pricing changes, but still have other resource updates a failure occurs:

│ Error: Error in function call
│ 
│   on .terraform/modules/pricing/modules/pricing/state_and_plan_content_from_json.tf line 59, in locals:
│   59:   instances_stripped_keys = local.input_type == "empty" ? [] : concat([
│   60:     for k, v in local.instances_map :
│   61:     setproduct([k], keys(v))
│   62:   ]...)
│     ├────────────────
│     │ local.instances_map is object with no attributes
│ 
│ Call to function "concat" failed: at least one argument is required.

With this update instead you will correctly receive pricing changes of 0:

Changes to Outputs:
  + pricing_input_resources         = {}
  + pricing_pricing_per_resources   = {}
  + pricing_pricing_product_filters = {}
  + pricing_resource_quantity       = {}
  + pricing_resources               = {}
  + pricing_total_price_per_hour    = 0
  + pricing_total_price_per_month   = 0

Breaking Changes

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request

[antonbabenko]

Thanks for the PR! A minor comment and we are good to go.

[mkubilus]

Thanks for the PR! A minor comment and we are good to go.

I've tested this suggestion and verified that it resolves the original issue. Thanks!

[antonbabenko]

This PR is included in version 1.3.1 🎉

[github-actions]

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