versions: consolidate various types of Components

There used to be three definitions of a Component type, and conversion
routines between the three. Since the use case is always the same, and
the Component semantics are defined by versions.go and the installer, it
seems appropriate to define the Component type there and import it in
the necessary places.

internal/versions/components/components.proto

@@ -0,0 +1,19 @@
+syntax = "proto3";
+
+package components;
+
+option go_package = "github.com/edgelesssys/constellation/v2/internal/versions/components";
+
+// Component is a Kubernetes component to install.
+message Component {
+  // URL of the component. Usually, this would be an HTTP download link.
+  string url = 1;
+  // Hash contains the expected digest of the resource retrieved from the URL,
+  // in the format "<algo>:<hex-digest>".
+  string hash = 2;
+  // InstallPath is the path to install the component to.
+  string install_path = 3;
+  // Extract indicates whether the resource at above URL is an archive, such as
+  // a gzipped tarball, and should be extracted to the install_path.
+  bool extract = 4;
+}