[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

plugins/search/README.md

@@ -0,0 +1,9 @@
+# Backstage Search
+
+**This plugin is still under development.**
+
+You can follow the progress under the Global search in Backstage [milestone](https://github.com/backstage/backstage/milestone/21) or reach out to us in the #search Discord channel.
+
+## Getting started
+
+Run `yarn start` in the root directory, and then navigate to [/search](http://localhost:3000/search)to check out the plugin.