Hindawi fetching

[ErnestaP]

Add Hindawi publisher files fetching DAG. Important information for a task solution:

Fetching steps:

• Fetch data from API (response is in XML)
• Save it in s3
• Download from s3
• Split XML (downloaded XML consist of more than one article. Split means, one smaller XML - one article)
• Trigger runs of processing DAG. One run has to be triggered with one article. The response is XML, use ElementTree as a parsing lib

Expected behavior : Input: XML doc., which consists of more than one article. Output: trigger files processing DAG

Tests are mandatory

[ErnestaP]

Update: Anne approved the output

[drjova]

@ErnestaP double check that fetching is working as expected on QA