frontend-plugin-api: remove defineParams from PluginHeaderActionBlueprint

Replace the defineParams + createExtensionBlueprintParams pattern with
inline param types on the factory, matching PageBlueprint, SubPageBlueprint,
and other blueprints. Update the app-visualizer usage accordingly.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

.changeset/remove-plugin-header-action-define-params.md

@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-plugin-api': minor
+---
+
+**BREAKING**: Removed the `defineParams` callback from `PluginHeaderActionBlueprint`. Params are now typed inline on the factory, matching the pattern used by `PageBlueprint`, `SubPageBlueprint`, and others. To migrate, change `params: defineParams => defineParams({ ... })` to `params: { ... }` when calling `PluginHeaderActionBlueprint.make(...)`.

.changeset/update-app-visualizer-header-action.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-app-visualizer': patch
+---
+
+Updated `PluginHeaderActionBlueprint` usage to pass params as a plain object.