python,configs: Add Resource class to gem5 components

The `Resource` class can be used to obtain a gem5 resource. The
`Resource` class, via the `downloader` package, parses the gem5
resources `resources.json` file:
https://gem5.googlesource.com/public/gem5-resources/+/refs/heads/develop/resources.json
From this it can determine the available resources and where to download
them. This allows for automatic retrieval of resources.

The `CustomResource` can be used to specify a local resource not part of
gem5 resources.

The board's `set_workload` function has been updated to use the
resources.

The components library example scripts have been updated to demonstrate
the `Resource`/`CustomResource` class usage.

Issue-on: https://gem5.atlassian.net/browse/GEM5-1022
Change-Id: I59cfe81d5ec9c64576c0dab55af52aede96976fb
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/49304
Reviewed-by: Austin Harris <austin.dane.harris@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

configs/example/components-library/simple_binary_run.py

@@ -48,6 +48,7 @@ sys.path.append(
     )
 )
 
+from components_library.resources.resource import CustomResource
 from components_library.boards.simple_board import SimpleBoard
 from components_library.cachehierarchies.classic.no_cache import NoCache
 from components_library.memory.single_channel import SingleChannelDDR3_1600
@@ -76,9 +77,10 @@ motherboard.connect_things()
 
 # Set the workload
 thispath = os.path.dirname(os.path.realpath(__file__))
-binary = os.path.join(
-    thispath, "../../../tests/test-progs/hello/bin/x86/linux/hello"
-)
+binary = CustomResource(os.path.join(
+    thispath,
+    "../../../tests/test-progs/hello/bin/x86/linux/hello"
+))
 motherboard.set_workload(binary)