Merge branch 'master' of github.com:spotify/backstage into mob/prepare-from-catalog

* 'master' of github.com:spotify/backstage: (60 commits)
  packages,plugins: remove main:src and fix some main fields
  packages/config: added get and getOptional
  changed  down caret to be up caret on user profile in the sidebar
  packages/config: add getOptionalConfig and getOptionalConfigArray to mirror other accessors
  packages/config-loader,core: update config usage to include context
  build(deps): bump @types/react from 16.9.25 to 16.9.37 (#1342)
  build(deps): bump rollup-plugin-esbuild from 2.0.0 to 2.1.0 (#1361)
  build(deps-dev): bump lint-staged from 10.2.9 to 10.2.11 (#1359)
  Polishing the Create page (#1353)
  Add some air between sidebar sections (#1355)
  Starred icon is yellow (#1351)
  Updated FAQ with Gitlab link (#1352)
  build(deps): bump react-helmet from 6.0.0 to 6.1.0 (#1327)
  packages/config: added context to keep track of where config is from for error messages
  packages/config: added .keys()
  packages/config: keep track of key prefix to display better error messages
  packages/config: optimize some error message handling
  packages/config: allow config readers to be backed by undefined data
  packages/config: flip around must* and get* to get* and getOptional*
  packages/core-api: fix invocation order when continuing to app after sign-in
  ...

docs/FAQ.md

@@ -15,12 +15,12 @@ No, but it can be! Backstage is designed to be a developer portal for all your
 infrastructure tooling, services, and documentation. So, it's not a monitoring
 platform — but that doesn't mean you can't integrate a monitoring tool into
 Backstage by writing
-[a plugin](https://github.com/spotify/faq#what-is-a-plugin-in-backstage).
+[a plugin](https://github.com/spotify/backstage/blob/master/docs/FAQ.md#what-is-a-plugin-in-backstage).
 
 ### How is Backstage licensed?
 
-Backstage was released as free and open software by Spotify and is licensed
-under [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0).
+Backstage was released as open sourced software by Spotify and is licensed under
+[Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0).
 
 ### Why did we open source Backstage?
 
@@ -99,15 +99,15 @@ plugins. ​
 
 ### What is a "plugin" in Backstage?
 
-​ Plugins are what provide the feature functionality in Backstage. They are used
-to integrate different systems into Backstage's frontend, so that the developer
-gets a consistent UX, no matter what tool or service is being accessed on the
-other side. ​ Each plugin is treated as a self-contained web app and can include
-almost any type of content. Plugins all use a common set of platform APIs and
-reusable UI components. Plugins can fetch data either from the backend or an API
-exposed through the proxy. ​ Learn more about
-[the different components](https://github.com/spotify/backstage#overview) that
-make up Backstage. ​
+By far, our most-used plugin is our TechDocs plugin, which we use for creating
+technical documentation. Our philosophy at Spotify is to treat "docs like code",
+where you write documentation using the same workflow as you write your code.
+This makes it easier to create, find, and update documentation. We hope to
+release
+[the open source version](https://github.com/spotify/backstage/issues/687) in
+the future. (See also:
+"[Will Spotify's internal plugins be open sourced, too?](https://github.com/spotify/backstage/blob/master/docs/FAQ.md#what-is-a-plugin-in-backstage)"
+above)
 
 ### Do I have to write plugins in TypeScript?
 
@@ -156,10 +156,12 @@ Integrators also configure closed source plugins locally from the monorepo. ​
 ​ We chose GitHub because it is the tool that we are most familiar with, so that
 will naturally lead to integrations for GitHub being developed at an early
 stage. ​ Hosting this project on GitHub does not exclude integrations with
-alternatives, such as GitLab or Bitbucket. We believe that in time there will be
-plugins that will provide functionality for these tools as well. Hopefully,
-contributed by the community! ​ Also note, implementations of Backstage can be
-hosted wherever you feel suits your needs best. ​
+alternatives, such as
+[GitLab](https://github.com/spotify/backstage/issues?q=is%3Aissue+is%3Aopen+GitLab)
+or Bitbucket. We believe that in time there will be plugins that will provide
+functionality for these tools as well. Hopefully, contributed by the community!
+​ Also note, implementations of Backstage can be hosted wherever you feel suits
+your needs best. ​
 
 ### Who maintains Backstage?