[COMPLIANCE] Add copyright and license headers

[bendbennett]

Closes #93

This PR introduces:

• modification to make generate command that will auto-generate documentation and all copyright headers for this repo (hooks into go generate)
• GH workflow that will error if copyright headers aren't present or if license is malformed
• Addition to the CONTRIBUTING.md on how to run license autogenerating commands
• Add new copywrite module and add to dependabot

[austinvalle]

You might need to run a go mod tidy on this? Was expecting terraform-plugin-docs and copywrite to be dependencies here

[austinvalle]

Running into a similar thing with terraform-plugin-go with it's own tools directory. Adding tools as it's own module will remove terraform-plugin-docs from the root go.mod next time you run go mod tidy.

If the doc tool is removed from the root go.mod, then you'll get this error running go generate:

 $ go generate ./...  

no required module provides package github.com/hashicorp/terraform-plugin-docs/cmd/tfplugindocs; to add it:
        go get github.com/hashicorp/terraform-plugin-docs/cmd/tfplugindocs
main.go:20: running "go": exit status 1

[bendbennett]

I've just switched to using separate directories for copywrite and tools. Seems to be behaving as desired.

[austinvalle]

Cool 👍🏻, I'll follow suit in terraform-plugin-go

[bflad]

Looks great to me 🚀 Excited for cleaner Go modules. 🧹

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active contributions.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.