Deprecate config.yaml as valid config source; Add unit regression for correct config paths (#1640)

Warn user of future deprecation of ./config.yaml for v1.0.0 release

---------

Signed-off-by: Aidan Delaney <adelaney21@bloomberg.net>
Signed-off-by: Christopher Phillips <christopher.phillips@anchore.com>
Co-authored-by: Christopher Phillips <christopher.phillips@anchore.com>

internal/config/test-fixtures/.syft.yaml

@@ -0,0 +1,7 @@
+# same as --file; write output report to a file (default is to write to stdout)
+file: "test-explicit-config"
+package:
+  cataloger:
+    scope: "squashed"
+
+    # same as --scope; limit the scope of the cataloger to only the specified types

internal/config/test-fixtures/config-dir-test/.syft/config.yaml

@@ -0,0 +1,5 @@
+# same as --file; write output report to a file (default is to write to stdout)
+file: "test-dir-config"
+package:
+  cataloger:
+    scope: "squashed"

internal/config/test-fixtures/config-home-test/.syft/config.yaml

@@ -0,0 +1,5 @@
+# same as --file; write output report to a file (default is to write to stdout)
+file: "test-home-XDG-config"
+package:
+  cataloger:
+    scope: "squashed"

internal/config/test-fixtures/config-home-test/config-file/.syft.yaml

@@ -0,0 +1,5 @@
+# same as --file; write output report to a file (default is to write to stdout)
+file: "test-home-config"
+package:
+  cataloger:
+    scope: "squashed"

internal/config/test-fixtures/config-wd-file/.syft.yaml

@@ -0,0 +1,5 @@
+# same as --file; write output report to a file (default is to write to stdout)
+file: "test-wd-named-config"
+package:
+  cataloger:
+    scope: "squashed"