docs(changeset): Adopt new MiddlewareHandlers type for simplicity, an…

…d in doing so fix type of middleware (for plugins) that incorrectly unwrapped promise resulting in TypeScript incorrectly suggesting that `await` was not necessary.

.changeset/mean-mugs-hide.md

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+---
+"grafserv": patch
+---
+
+Adopt new MiddlewareHandlers type for simplicity, and in doing so fix type of
+middleware (for plugins) that incorrectly unwrapped promise resulting in
+TypeScript incorrectly suggesting that `await` was not necessary.