Add central docs for hip implementation

[exploreriii]

Leaving a note from TSC call 28/07/2026 that conversation may still be ongoing

It may be worth adding a central place where we document HIP progress.

A maintainer from one repository makes a PR that changes the flag from not implemented --> implemented for a given HIP.

This means we can have reliable awareness across Hiero for HIP implementation progress.

Alternatively, maintainers may be encouraged to maintain their own HIP tracking within their repo.

[aceppaluni]

/assign

[exploreriii]

@aceppaluni note the issue is not 'confirmed' but feel free to have a go at it and perhaps we can discuss again on the TSC with a working model