minor modification to move the top_k param to the environment variables for convenience.

[ppmarkus]

Depending on the use case we generally require many more rows to be returned.

[MohammadrezaPourreza]

@ppmarkus Thanks for your contribution we really appreciate all your help.
Since agent also has a tool to run a SQL query we have to also make the following change to the dataherald_sqlagent.py file:
TOP_K = os.getenv("MAX_QUERY_RETURN_ROWS", "50"))
Could you please also include this in your PR?

[ppmarkus]

updated and tested before and after.
Without UPPER_LIMIT_QUERY_RETURN_ROWS env, rows limited to 50.
When set, returned rows changed up to new set limit.
Casting env var to int was necessary, otherwise got error: unsupported operand type(s) for +: 'int' and 'str' because top_k needs to be an int.