docs(instructions): document autorelease convention for locally-authored specs

[WithEnoughCoffee]

Summary

Adds a new Repository Hygiene Rule to .github/copilot-instructions.md documenting the team convention that locally-authored specs should use %autorelease/%autochangelog rather than a static Release: with a hand-written %changelog.

This was originally proposed as part of the telegraf PR (#17798), but per review feedback from @tobiasb-ms it was split out into its own PR so the convention change is reviewed independently of the telegraf packaging work.

Change

Item 6 under Repository Hygiene Rules:

New specs use autorelease: For any spec we author ourselves (local specs), use %autorelease and %autochangelog rather than a static Release: with a hand-written %changelog. Set the component's release = { calculation = "autorelease" } in its .comp.toml so azldev preserves and expands the macros. This is the team convention for newly authored specs even though it differs from upstream-Fedora overlay handling.

Docs-only change; no build impact.

[Copilot]

Pull request overview

This PR adds a single new item (rule #6) to the Repository Hygiene Rules section of .github/copilot-instructions.md, documenting the team convention that locally-authored specs should use rpmautospec's %autorelease/%autochangelog macros with release = { calculation = "autorelease" } rather than a static Release: and hand-written %changelog. It is a docs-only change with no build impact, split out from the telegraf PR (#17798) so the convention can be reviewed independently.

I verified the technical claims:

• "autorelease" is a valid value for release.calculation (enum in external/schemas/azldev.schema.json:835-840) and is already used in-tree (e.g. base/comps/samba/samba.comp.toml:3, base/comps/gvisor-tap-vsock/gvisor-tap-vsock.comp.toml:5).
• %autorelease/%autochangelog are the correct rpmautospec macro names and appear across rendered specs.
• The new bullet's formatting (bold prefix + colon) matches the surrounding rules 1–5.

Changes:

• Add hygiene rule #6 instructing that self-authored/local specs use %autorelease/%autochangelog and set release = { calculation = "autorelease" }.