Add support for customizable icons in SearchResultListItemBlueprint and related components

Signed-off-by: Andreas Berger <andreas@berger-ecommerce.com>

plugins/techdocs/report-alpha.api.md

@@ -322,6 +322,7 @@ const _default: OverridableFrontendPlugin<
         {
           predicate?: SearchResultItemExtensionPredicate;
           component: SearchResultItemExtensionComponent;
+          icon?: JSX_2.Element;
         },
         'search.search-result-list-item.item',
         {}
@@ -365,6 +366,7 @@ export const techDocsSearchResultListItemExtension: ExtensionDefinition<{
     {
       predicate?: SearchResultItemExtensionPredicate;
       component: SearchResultItemExtensionComponent;
+      icon?: JSX_2.Element;
     },
     'search.search-result-list-item.item',
     {}

plugins/techdocs/src/alpha/index.tsx

@@ -55,6 +55,7 @@ import {
 } from '@backstage/plugin-techdocs-react';
 
 import { useTechdocsReaderIconLinkProps } from './hooks/useTechdocsReaderIconLinkProps';
+import { DocsIcon } from '@backstage/core-components';
 
 /** @alpha */
 const techdocsEntityIconLink = EntityIconLinkBlueprint.make({
@@ -116,6 +117,7 @@ export const techDocsSearchResultListItemExtension =
     },
     factory(originalFactory, { config }) {
       return originalFactory({
+        icon: <DocsIcon />,
         predicate: result => result.type === 'techdocs',
         component: async () => {
           const { TechDocsSearchResultListItem } = await import(