Add batching in matcher.py

[woodthom2]

Related to issue #56

There is another entry point where the LLM is used which is in matcher.py
-> https://github.com/harmonydata/harmony/blob/main/src/harmony/matching/matcher.py#L131

Please can you allow the batch size to be set in an environment variable BATCH_SIZE. If BATCH_SIZE is not set (either empty or null) then we default to 50.

Please add unit tests. E.g. set batch size to 5 and send 10 items to Harmony, check that they are divided into 2 batches of 5+5? If you can add any new unit tests to the folder that would be great