text: Title: [new]: `get_value(key_value_items, key)`
  Body: ### Check the idea has not already been suggested
  
  - [X] I could not find my idea in [existing issues](https://github.com/unytics/bigfunctions/issues?q=is%3Aissue+is%3Aopen+label%3Anew-bigfunction)
  
  ### Edit the title above with self-explanatory function name and argument names
  
  - [X] The function name and the argument names I entered in the title above seems self explanatory to me.
  
  ### BigFunction Description as it would appear in the documentation
  
  Return `value` at key `key` from `key_value_items` array
  
  ### Examples of (arguments, expected output) as they would appear in the documentation
  
  - `get_value([struct("k" as key, 1 as value)], "k")` --> `1`
  - `get_value([struct("k" as key, 1 as value)], "a")` --> `null`