Edit delete_test_snippets script

What does this MR do and why?

Describe in detail what your merge request does and why.

Edits cleanup script for snippets to limit the number of items per page in the request and to stop if the number of pages is too high. This way it can cope with large amounts of snippets per user. Currently we have several thousands of historic test snippets in staging and production and the script fails to run as it receives 500 on api request. We will delete them in batches by implementing a scheduled job.

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