Implement a LICENSE rule type

[rdimitrov]

The following rule type allows for:

• Ensuring only the presence of a LICENSE file (when license_type = "" is left blank)

---
# Sample profile for validating the presence of a license file
version: v1
type: profile
name: license
context:
  provider: github
repository:
  - type: license
    def:
      license_filename: LICENSE
      license_type: ""

• Ensuring the present LICENSE file contains a given license type, i.e. Apache.

---
# Sample profile for validating the presence of a license file and its type
version: v1
type: profile
name: license
context:
  provider: github
repository:
  - type: license
    def:
      license_filename: LICENSE
      license_type: "Apache"

• The file name of the license is not hardcoded to allow for flexibility
• The licence type check just verifies if the configured keyword is present in the license file. It doesn't ensure that the legal content in that file matches the configured license type.

Motivated by the discussion in #1413 (comment)

[eryn-muetzel]

@rdimitrov it would be better to have someone in engineering review this PR

[rdimitrov]

@rdimitrov it would be better to have someone in engineering review this PR

yeah, I added you just so you are aware of the functionality 👍