Refactor settings file path handling

[pdekkers]

Description

The added method centralizes the logic for constructing the path to the settings JSON file.

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No

[Copilot]

Pull Request Overview

This PR refactors the logic for constructing the settings JSON file path by introducing a centralized helper method.

• Replaces multiple inline usages of Path.Combine for ".aspire/settings.json" with a single helper method.
• Updates various components across the project (ConfigurationHelper, ProjectLocator, Program, and ConfigurationService) to use the new method for consistency.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/Aspire.Cli/Utils/ConfigurationHelper.cs	Introduces BuildPathToSettingsJsonFile to centralize settings file path creation.
src/Aspire.Cli/Projects/ProjectLocator.cs	Refactors inline path building to use the new helper method.
src/Aspire.Cli/Program.cs	Replaces path construction with the helper method.
src/Aspire.Cli/Configuration/ConfigurationService.cs	Updates both settings file lookup and creation to use the centralized logic.

[mitchdenny]

LGTM. Thanks for the contribution especially on a relatively new part of the code base!