Rename SourceName to SourceSpec

[amarjandu]

This was a FIXME that was part of a sketch done by @hannes-ucsc
See #2650 (comment)

Index: src/azul/indexer/__init__.py
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/src/azul/indexer/__init__.py b/src/azul/indexer/__init__.py
--- a/src/azul/indexer/__init__.py	(revision 46e23043c6a4421f588ce3ac9f17db488ae4c88a)
+++ b/src/azul/indexer/__init__.py	(date 1614202583703)
@@ -53,6 +53,9 @@
 SOURCE_NAME = TypeVar('SOURCE_NAME', bound='SourceName')
 
 
+# FIXME: Rename to SourceSpec/SOURCE_SPEC, and all .name to .spec
+#        <insert link to ticket here>
+
 class SourceName(ABC, Generic[SOURCE_NAME]):
     """
     The name of a repository source containing bundles to index. A repository

[amarjandu]

pushed this into in-progress during parking lot discussion w/ @hannes-ucsc .

This should be fixed before addressing #2750

[hannes-ucsc]

For demo, show source specifications in manifests and JSON responses, as well as a sampling of contributions and aggregate documents (using Kibana).