Update youtube.py - Fix metadata validation error in YoutubeLoader (#5479)

This commit addresses a ValueError occurring when the YoutubeLoader
class tries to add datetime metadata from a YouTube video's publish
date. The error was happening because the ChromaDB metadata validation
only accepts str, int, or float data types.

In the `_get_video_info` method of the `YoutubeLoader` class, the
publish date retrieved from the YouTube video was of datetime type. This
commit fixes the issue by converting the datetime object to a string
before adding it to the metadata dictionary.

Additionally, this commit introduces error handling in the
`_get_video_info` method to ensure that all metadata fields have valid
values. If a metadata field is found to be None, a default value is
assigned. This prevents potential errors during metadata validation when
metadata fields are None.

The file modified in this commit is youtube.py.

# Your PR Title (What it does)

<!--
Thank you for contributing to LangChain! Your PR will appear in our
release under the title you set. Please make sure it highlights your
valuable contribution.

Replace this with a description of the change, the issue it fixes (if
applicable), and relevant context. List any dependencies required for
this change.

After you're done, someone will review your PR. They may suggest
improvements. If no one reviews your PR within a few days, feel free to
@-mention the same people again, as notifications can get lost.

Finally, we'd love to show appreciation for your contribution - if you'd
like us to shout you out on Twitter, please also include your handle!
-->

<!-- Remove if not applicable -->

Fixes # (issue)

## Before submitting

<!-- If you're adding a new integration, please include:

1. a test for the integration - favor unit tests that does not rely on
network access.
2. an example notebook showing its use


See contribution guidelines for more information on how to write tests,
lint
etc:


https://github.com/hwchase17/langchain/blob/master/.github/CONTRIBUTING.md
-->

## Who can review?

Community members can review the PR once tests pass. Tag
maintainers/contributors who might be interested:

<!-- For a quicker response, figure out the right person to tag with @

  @hwchase17 - project lead

  Tracing / Callbacks
  - @agola11

  Async
  - @agola11

  DataLoaders
  - @eyurtsev

  Models
  - @hwchase17
  - @agola11

  Agents / Tools / Toolkits
  - @vowelparrot

  VectorStores / Retrievers / Memory
  - @dev2049

 -->

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

langchain/document_loaders/youtube.py

@@ -231,13 +231,15 @@ class YoutubeLoader(BaseLoader):
             )
         yt = YouTube(f"https://www.youtube.com/watch?v={self.video_id}")
         video_info = {
-            "title": yt.title,
-            "description": yt.description,
-            "view_count": yt.views,
-            "thumbnail_url": yt.thumbnail_url,
-            "publish_date": yt.publish_date,
-            "length": yt.length,
-            "author": yt.author,
+            "title": yt.title or "Unknown",
+            "description": yt.description or "Unknown",
+            "view_count": yt.views or 0,
+            "thumbnail_url": yt.thumbnail_url or "Unknown",
+            "publish_date": yt.publish_date.strftime("%Y-%m-%d %H:%M:%S")
+            if yt.publish_date
+            else "Unknown",
+            "length": yt.length or 0,
+            "author": yt.author or "Unknown",
         }
         return video_info