Add ADR on storing copyright and license info in Aspect Models

[atextor]

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Description

Adds a decision record detailing how copyright and license information is stored
in Aspect Models.

Fixes #300.

Type of change

Please delete options that are not relevant.

• Clarification/documentation

Checklist:

• [-] My code follows the style guidelines of this project
• I have performed a self-review of my own code
• [-] I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• [-] I have added tests that prove my fix is effective or that my feature works

[Yauhenikapl]

LGTM!