Add fiscal sponsor projects to the site

[NPDebs]

This PR fixes issue #869. OLS's index fiscally sponsored community, RSE-AUNZ, has been added to the appropriate page (i.e .../open-incubator/fiscal-hosting/).

Changes made:

• Created a new fiscal_communities array within the _data/community.yaml file and added data about RSE-AUNZ.
• Wrote logic to add RSE-AUNZ to the bottom of the fiscal-hosting page.

Screenshot:

Note for reviewers:

• Does this count as mvp or robust structure (as requested in issue #870)?

Thanks for the review!

FOR CONTRIBUTOR

• [x] I have read the CONTRIBUTING.md document

PR Type:

• [ ] This PR adds a new blog post
• [x] This PR does something else (explain above)

FOR REVIEWERS

Thanks for taking the time to review! :heart:

Here are the list of things to make sure of:

• [ ] The website builds (a check will fail if not)
• [ ] All images have been added within the Pull Request and they have Alt text
• [ ] If there are paragraphs or text, the key messages are highlighted
• [ ] All internal links (within OLS website) use the {% link path_to_file.md %} format
• [ ] The preview corresponds to the changes described in the Pull Request
• [ ] The code is tidy and passes the linting tests

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