terraform: support required_version upgrades

[bschaatsbergen]

This is still a draft, but the goal is to add support for proposing Terraform core version upgrades via Dependabot by updating the required_version in a Terraform configuration file.

This pull request proposes:

• A new ReleasesClient to interface with the HashiCorp Release API, providing the ability to retrieve Terraform Core versions. Since Core versions are not available via the Terraform Registry, this client is necessary for version querying. Additionally, all provider binaries are released through this API, offering a potential path to consolidate provider dependency checking under this client in the future.
• Tbd.
• Tbd.

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.