Added support for checksum and checksum_value

[rtuk]

This allows the module to download remote files (http) without triggering a change every time puppet runs

Summary

Provide a detailed description of all the changes present in this pull request.

Additional Context

Add any additional context about the problem here.

• Root cause and the steps to reproduce. (If applicable)
  If you download a key from a keyserver (for example https://keyserver.ubuntu.com/pks/lookup?op=get&search=0xd6811ed3adeeb8441af5aa8f4528b6cd9e61ef26), the keyring is downloaded every time
  When providing the checksum of the contents of the expected file, a change is only triggered if the version on disk has changed.
• Thought process behind the implementation.

Related Issues (if any)

Mention any related issues or pull requests.

Checklist

• 🟢 Spec tests.
• 🟢 Acceptance tests.
• Manually verified. (For example puppet apply)