Write a function convstrs that will receive a char matrix of characters and a character ‘u’ or ‘l’. if the character is ‘u’, it will return a new char matrix with all of the characters in uppercase. if the character is ‘l’, it will return a new char matrix with all of the characters in lowercase. if the character is neither ‘u’ nor ‘l’, the char matrix that is returned will be identical to the input char matrix.