feat: add support for iso_url in builder configuration

[tenthirtyam]

Summary of Pull Request

Add support for iso_url in the builder configuration blocks.

The project supports configuring the ISO from either a datastore or URL source. By default, the project uses the datastore source.

If you are using a URL source to obtain your guest operating system .iso files, you must update the input variables to use the URL source.

Update the iso_url variable to download the .iso from a URL. The iso_url variable takes presedence over any other iso_* variables.

Example: builds/<type>/<build>/*.auto.pkvars.hcl

iso_url = "https://artifactory.rainpole.io/iso/linux/photon/4.0/x86_64/photon-4.0-xxxxxxxxx.iso"

Signed-off-by: Ryan Johnson johnsonryan@vmware.com

Type of Pull Request

• This is a bugfix.
• This is an enhancement or feature.
• This is a code style / formatting update.
• This is a documentation update.
• This is a refactoring update.
• This is something else.
  Please describe:

Related to Existing Issues

Closes: #235

Test and Documentation Coverage

• Tests have been completed (for bugfixes / features).
• Documentation has been added / updated (for bugfixes / features).

Breaking Changes?

• Yes, there are breaking changes.
• No, there are no breaking changes.

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