[Feature] Allow Metadata in Grants

Use case

From this pull request https://github.com/juanfont/headscale/pull/2764 there was a feature added to ignore fields that begin with "#" and treat them as benign data. Preservation without validation. This works great and allows GUI designers to store bits of metadata inside the policy entries themselves without feeling like an encroachment on other field validation duties.

Description

As of right now, this works perfectly with ACLs but not Grants.

For example, headscale-admin uses "#ha-meta" inside of the ACLs:

However, with Grants, this fails:

Would it be possible to have a similar enforcement where keys beginning with "#" are essentially ignored?

Thank you!

Contribution

• I can write the design doc for this feature
• I can contribute this feature

How can it be implemented?

No response