[WIP do not merge] fixes issue 140, adds hyphen to Apache-2.0 License

[RobertKielty]

Adds a hyphen to "Apache 2.0" in LICENSE.md to make it "Apache-2.0" so that it should resolve a CLO Monitor report that open-gitops is missing a License https://clomonitor.io/projects/cncf/open-gitops#project_license

[RobertKielty]

Hi, I would like to test this in a local copy of CLO Monitor first.

[williamcaban]

From what I gather from:

• https://www.apache.org/licenses/LICENSE-2.0 and https://www.apache.org/licenses/LICENSE-2.0#apply
• https://spdx.org/licenses/Apache-2.0.html

The correct SPDX short identifier is Apache-2.0 so this might be a good fix to correct the syntax.