fix: add check for interleavedContent (#1973)

# What does this PR do?
Checks for RAGDocument of type InterleavedContent

I noticed when stepping through the code that the supported types for
`RAGDocument` included `InterleavedContent` as a content type. This type
is not checked against before putting the `doc.content` is regex matched
against. This would cause a runtime error. This change adds an explicit
check for type.

The only other part that I'm unclear on is how to handle the
`ImageContent` type since this would always just return `<image>` which
seems like an undesired behavior. Should the `InterleavedContent` type
be removed from `RAGDocument` and replaced with `URI | str`?

## Test Plan


[//]: # (## Documentation)

---------

Signed-off-by: Kevin <kpostlet@redhat.com>

llama_stack/providers/utils/memory/vector_store.py

@@ -118,27 +118,25 @@ async def content_from_doc(doc: RAGDocument) -> str:
     if isinstance(doc.content, URL):
         if doc.content.uri.startswith("data:"):
             return content_from_data(doc.content.uri)
-        else:
-            async with httpx.AsyncClient() as client:
-                r = await client.get(doc.content.uri)
-            if doc.mime_type == "application/pdf":
-                return parse_pdf(r.content)
-            else:
-                return r.text
-
-    pattern = re.compile("^(https?://|file://|data:)")
-    if pattern.match(doc.content):
-        if doc.content.startswith("data:"):
-            return content_from_data(doc.content)
-        else:
+        async with httpx.AsyncClient() as client:
+            r = await client.get(doc.content.uri)
+        if doc.mime_type == "application/pdf":
+            return parse_pdf(r.content)
+        return r.text
+    elif isinstance(doc.content, str):
+        pattern = re.compile("^(https?://|file://|data:)")
+        if pattern.match(doc.content):
+            if doc.content.startswith("data:"):
+                return content_from_data(doc.content)
             async with httpx.AsyncClient() as client:
                 r = await client.get(doc.content)
             if doc.mime_type == "application/pdf":
                 return parse_pdf(r.content)
-            else:
-                return r.text
-
-    return interleaved_content_as_str(doc.content)
+            return r.text
+        return doc.content
+    else:
+        # will raise ValueError if the content is not List[InterleavedContent] or InterleavedContent
+        return interleaved_content_as_str(doc.content)
 
 
 def make_overlapped_chunks(document_id: str, text: str, window_len: int, overlap_len: int) -> list[Chunk]: