Prefix copyright text with SPDX tag

[adam-moss]

Currently the copyright text is provided as a comment.

In the same way the license is prefixed with the SPDX-License-Identifer: tag, should this be prefixed with the SPDX-FileCopyrightText: tag per https://spdx.github.io/spdx-spec/v2.3/file-tags/#h2-file-tags-format ?

[adam-moss]

@CalebAlbers can I get some thoughts on this please?

[CalebAlbers]

@adam-moss apologies for the delay. I've transitioned to a different team internally and @dlaguerta has the final say on things now, but I'm happy to provide some thoughts.

Generally speaking, I'm 100% in favor of this. Supporting the SPDX-compliant tag makes sense. I do think we should make it an optional thing, though, as (for better or worse) copywrite is used across a few thousand projects both internal and external to HashiCorp and switching to the SPDX-FileCopyrightText tag would be a breaking change.

Perhaps we can update #40 to use a config/command-line flag for now, and then consider switching the default behavior along with other changes in a v2 release?