Fix multi-region provider aliases generating incorrect Terraform JSON format

[Copilot]

When configuring providers with dot-notation aliases (e.g., aws.use1), the generated providers_override.tf.json emitted invalid structure — separate top-level keys instead of the array-of-objects format Terraform's JSON syntax requires for multiple provider instances.

Changes

• pkg/terraform/output/backend.go: Added exported ProcessProviderAliases that detects dot-notation provider keys, groups all configurations for the same provider type into an array (base config first, aliases sorted), and leaves non-aliased providers unchanged
• internal/exec/utils.go: Updated generateComponentProviderOverrides to delegate to tfoutput.ProcessProviderAliases, eliminating duplicated logic

Example

Given stack config:

providers:
  aws:
    region: us-east-2
  aws.use1:
    region: us-east-1
    alias: use1

Before:

{ "provider": { "aws": { "region": "us-east-2" }, "aws.use1": { "alias": "use1", "region": "us-east-1" } } }

After:

{
  "provider": {
    "aws": [
      { "region": "us-east-2" },
      { "alias": "use1", "region": "us-east-1" }
    ]
  }
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Multi-Region with Provider Aliases example is not working</issue_title>
<issue_description>### Describe the Bug

https://atmos.tools/stacks/providers#multi-region-with-provider-aliases, this example is not working, the actual generated file is different from the example.

Expected Behavior

The generated file is the same as the example.

Steps to Reproduce

With the following atmos component config:

components:
  terraform:
    eip:
      providers:
        aws:
          region: us-east-2
        aws.use1:
          region: us-east-1
          alias: use1
      metadata:
        component: eip

Run atmos command and check the output of providers_override.tf.json

Screenshots

The content of the generated providers_override.tf.json

{
  "provider": {
    "aws": {
      "region": "us-east-2"
    },
    "aws.use1": {
      "alias": "use1",
      "region": "us-east-1"
    }
  }
}

Would expect it to be :

{
  "provider": {
    "aws": [
      {
        "region": "us-east-2"
      },
      {
        "alias": "use1",
        "region": "us-east-1"
      }
    ]
  }
}

Environment

• OS: OSX
• Version: 1.209.0
• Terraform version: v1.14.7

Additional Context

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Multi-Region with Provider Aliases example is not working #2208

---

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[github-actions]

Dependency Review

✅ No vulnerabilities or license issues found.

Scanned Files

None

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.40%. Comparing base (1f4ac96) to head (b716bc3).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2210   +/-   ##
=======================================
  Coverage   77.40%   77.40%           
=======================================
  Files         962      962           
  Lines       91284    91314   +30     
=======================================
+ Hits        70657    70686   +29     
+ Misses      16550    16548    -2     
- Partials     4077     4080    +3     

Flag	Coverage Δ
unittests	77.40% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
internal/exec/utils.go	82.31% <100.00%> (ø)
pkg/terraform/output/backend.go	82.47% <100.00%> (+7.84%)	⬆️

... and 6 files with indirect coverage changes

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