Add CLI to manage encrypted files/configs.

To edit/show encrypted file:

```
bin/rails encrypted:edit config/staging_tokens.yml.enc
bin/rails encrypted:edit config/staging_tokens.yml.enc --key config/staging.key
bin/rails encrypted:show config/staging_tokens.yml.enc
```

Also provides a backing Rails.application.encrypted API for Ruby access:

```ruby
Rails.application.encrypted("config/staging_tokens.yml.enc").read
Rails.application.encrypted("config/staging_tokens.yml.enc").config
Rails.application.encrypted("config/staging_tokens.yml.enc", key: "config/staging.key")
```

1 files changed, 4 insertions, 1 deletions

diff --git a/railties/test/commands/credentials_test.rb b/railties/test/commands/credentials_test.rb
index 743fb5f788..4ef827fcf1 100644
--- a/railties/test/commands/credentials_test.rb
+++ b/railties/test/commands/credentials_test.rb
@@ -13,7 +13,10 @@ class Rails::Command::CredentialsCommandTest < ActiveSupport::TestCase
   teardown { teardown_app }
 
   test "edit without editor gives hint" do
-    assert_match "No $EDITOR to open credentials in", run_edit_command(editor: "")
+    run_edit_command(editor: "").tap do |output|
+      assert_match "No $EDITOR to open file in", output
+      assert_match "bin/rails credentials:edit", output
+    end
   end
 
   test "edit credentials" do