And so it continues for the entire file, so it is only required to input the pattern with the opening bracket?
Yes. Understanding how the multiline codec is supposed to work is essential.
Is it still required to also have a filter section for this file?
If you want to parse the data further, yes.
I have tried the following config however it does not produce any output:
That's because Logstash is tailing the file. Read about sincedb in the file input documentation and study the start_position, sincedb_path, and ignore_older options.