[jupyter] add memory example to sql_db agent

[skcoirz]

• Memory can largely enrich Agent convenience.
• This PR added an example showing how to use Memory in SQL DB Agent.
• Fixed a bug in the old SQLDatabaseToolkit initiation case as llm is a required input in the latest version.
• Re-tested several old examples to confirm everything works the same.

[dev2049]

should we be using gpt-4 in example? probably better to use something anyone can access (unless the example doesn't work with anything else)

[skcoirz]

should we be using gpt-4 in example? probably better to use something anyone can access (unless the example doesn't work with anything else)

sure, have updated to use gpt-3.5-turbo

[graemeglass]

should we be using gpt-4 in example? probably better to use something anyone can access (unless the example doesn't work with anything else)

sure, have updated to use gpt-3.5-turbo

Since this PR hasn't been merged yet, you could change it back to gpt-4. It became publicly available on 6 July 2023.

[leo-gan]

@skcoirz Hi , could you, please, resolve the merging issues and address the last comments (if needed)? After that, ping me and I push this PR for the review. Thanks!