docs: add snippets for Matrix Factorization tutorials

[rey-esp]

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Fixes #<issue_number_goes_here> 🦕

[snippet-bot]

Here is the summary of changes.

You are about to add 6 region tags.

• samples/snippets/mf_explicit_model_test.py:19, tag bigquery_dataframes_bqml_mf_explicit_create_dataset
• samples/snippets/mf_explicit_model_test.py:26, tag bigquery_dataframes_bqml_mf_explicit_upload_movielens
• samples/snippets/mf_explicit_model_test.py:81, tag bigquery_dataframes_bqml_mf_explicit_create
• samples/snippets/mf_explicit_model_test.py:104, tag bigquery_dataframes_bqml_mf_explicit_evaluate
• samples/snippets/mf_explicit_model_test.py:111, tag bigquery_dataframes_bqml_mf_explicit_recommend_df
• samples/snippets/mf_explicit_model_test.py:124, tag bigquery_dataframes_bqml_mf_explicit_recommend_model

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[tswast]

Snippet bot failure looks like a real one:

• samples/snippets/mf_explicit_model_test.py:60, tag bigframes_dataframe_bqml_mf_explicit_recommend_df doesn't have a matching start tag.
• samples/snippets/mf_explicit_model_test.py:48, tag bigframes_dataframe_bqml_mf_recommend_df doesn't have a matching end tag.

Edit: I created a suggested commit that I think should fix that.

[tswast]

predicted here is only a subset. The SQL shows creating a table of all the predictions.

CREATE OR REPLACE TABLE `bqml_tutorial.recommend`
AS
SELECT
  *
FROM
  ML.RECOMMEND(MODEL `bqml_tutorial.mf_explicit`);

Did we implement a way for predict() to work without any inputs like in the SQL?

Suggested change

	# Load movies
	movies = bpd.read_gbq("bqml_tutorial.movies")
	# Merge the movies df with the previously created predicted df
	merged_df = bpd.merge(predicted, movies, left_on="item_id", right_on="movie_id")
	predicted = model.predict()
	# Load movies
	movies = bpd.read_gbq("bqml_tutorial.movies")
	# Merge the movies df with the previously created predicted df
	merged_df = bpd.merge(predicted, movies, left_on="item_id", right_on="movie_id")

[rey-esp]

This feature isn't supported yet and an issue will be filed shortly

[tswast]

Samples tests passed! 🥳