Corpus Management - v2 Empty state

What does this MR do and why?

Describe in detail what your merge request does and why.

This MR solves #347272 (closed)

1. In order to make empty state for corpus management consistent with other empty states of security configuration, I have created empty state component according to required design.
2. Previously adding new corpus via GlModal was a part of corpus-upload component and was used only in this component.
3. New empty state has to provide a button allowing us to create new corpus as well.
4. I have extracted add new corpus functionality to separate component and reused it in new empty state and old corpus- upload component via slots.
5. Tests were added and updated accordingly.
6. Backend was updated with extra property for new illustration

Screenshots or screen recordings

before

after

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Go to any project /root/$PROJECT/
2. Go to /root/$PROJECT/-/security/configuration
3. Scroll to bottom and select Manage Corpuses.
4. You will be at /root/$PROJECT/-/security/configuration/corpus_management.
5. If you already have corpuses, you should delete all in order to see empty state

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #347272 (closed)