Extract MediaStorage entity as parent to ImageStore

[obulat]

Fixes WordPress/openverse#1739

This PR extracts the data and methods from the ImageStore class that are common to all media types, and creates an Abstract base class called MediaStore.

MediaStore has the methods for validating the tags, metadata, license information, the resulting TSV rows, and for writing the buffer to the disk. It also has an abstract method, add_item, which will be implemented by all child classes (ImageStore currently, but AudioStore will be added shortly). This method will handle the validation of single item metadata.

This is the third iteration of adding audio :) This time, in parallel with the API, this PR only handles the MediaStore extraction, so it can be merged before we have a final decision on what Audio metadata we want to save.

All the data fields we currently collect for images from providers can be found in IMAGE_TSV_COLUMNS list. Here, they are listed in order they are written to TSV, and the fields that are common for all media are in bold:

• foreign_identifier
• foreign_landing_url
• image_url / audio_url (url in database)
• thumbnail_url
• width
• height
• filesize
• license_
• license_version
• creator
• creator_url
• title
• meta_data
• tags
• provider
• source
• ingestion_type

There are several ways this PR can be tested:

1. Build the docker containers and run all the tests on Docker:
   docker exec cc_catalog_airflow_webserver_1 /usr/local/airflow/.local/bin/pytest

or

2. Choose one of the provider API scripts, preferably the ones that don't require authentication, such as Cleveland museum or Science museum, and run the script by itself. After it finishes running, you should see the result in a .tsv file inside your /tmp folder. Hopefully, all fields collected should be written in the .tsv file.

or

3. In Pycharm, I right-click on src/cc_catalog_airflow/dags/common folder, and then select Run 'pytest in common' to run the tests only for the common module that was changed in the PR.

[zackkrida]

FYI, I'm hoping to review this tomorrow 😸