Add credential type icons

- Add keychain.png for keychain credential type
- Add raw.png for raw JSON credential type
- Update paths in credential_form_component.ex

Icons are placed in /priv/static/images/ alongside other static
images like user.png, google.png, etc. File names without dashes
avoid gitignore patterns that exclude digested build assets.

Author: elias-ba

lib/lightning_web/live/credential_live/credential_form_component.ex

@@ -1079,12 +1079,12 @@ defmodule LightningWeb.CredentialLive.CredentialFormComponent do
       {"Raw JSON", "raw",
        Routes.static_path(
          LightningWeb.Endpoint,
-         "/images/raw-square.png"
+         "/images/raw.png"
        ), nil},
       {"Keychain", "keychain",
        Routes.static_path(
          LightningWeb.Endpoint,
-         "/images/keychain-square.png"
+         "/images/keychain.png"
        ), nil}
     ])
     |> Enum.sort_by(&String.downcase(elem(&1, 0)), :asc)