[Search] Search frontend plugin (#3086)

* feat(search) search plugin

* feat(search): search page components

* feat(search): api

* feat(search): filters wip

* feat(search): wip filters

* fix(search): delete unused useParams hook

* fix(search): update docs

* fix(search): use latest versions of dependencies

* fix(search): change version of catalog plugin

* fix(search api): pass instance of catalog api to search api

* fix(filters): rename component from FilterButton to FiltersButton

* fixup

* fix(filters): use list of checkboxes to match style of catalog page filters

* fix(styles): use theme spacing for margins and paddings, delete unused styles

* fix(search): change terminology of search input to be more consistent and clear

* fix(search): restructure component exports according to ADR

* fix(search): replace sm with xs on Grid components to support smaller screens

* fix(search): add types

* fixup

* fix(search): bump backstage core

* change versions of backstage theme and dev-utils

packages/app/package.json

@@ -25,6 +25,7 @@
     "@backstage/plugin-rollbar": "^0.2.1",
     "@backstage/plugin-scaffolder": "^0.3.0",
     "@backstage/plugin-sentry": "^0.2.1",
+    "@backstage/plugin-search": "^0.2.0",
     "@backstage/plugin-tech-radar": "^0.3.0",
     "@backstage/plugin-techdocs": "^0.2.1",
     "@backstage/plugin-user-settings": "^0.2.1",