Introduce a new field to enable linking issues

[darkwisebear]

Introduce field to link issues

Since we want to introduce different rule tiers, we also need to enable the guideline users to quickly identify rules that are superseded by other rules to assist them during project tailoring.

Introduce a field (freeform) that allows for linking one issue to another. It shall be of the form : , where LINKTYPE is fulfills or is-fulfilled-by, and references another SCRC guideline.

Todo

• Add field to https://github.com/PLeVasseur/safety-critical-rust-coding-guidelines/blob/main/.github/ISSUE_TEMPLATE/CODING-GUIDELINE.yml
• Add description of the link types and reason why doing so to https://github.com/PLeVasseur/safety-critical-rust-coding-guidelines/blob/main/CONTRIBUTING.md
• Inspect guidelines for possible candidates and create a PR with the links in place