added upload and download aliases in csv format.

[Faakhir30]

Refers #1812

Closes #1793

Using content negotiation for PUT, GET aliases service.

• send the "Accept" HTTP header "text/csv" for get request to download aliases as csv. Then REST API would return the CSV file.
• send the "Content-Type" HTTP header "text/csv" for post request to add aliases from csv.

Tasks breakdown:

• Handle text/csv content-type to upload aliases in bulk.
• Handle text/csv content-type to download aliases.
• Add new http-examples
• Add aliases unit/integration tests to plone.restapi.
• Add/update documentation
• Deal filters in download functionality in controlpannel of Products.CMFPlone, filters not being applied yet.

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📚 Documentation preview 📚: https://plonerestapi--1813.org.readthedocs.build/

[mister-roboto]

@Faakhir30 thanks for creating this Pull Request and helping to improve Plone!

TL;DR: Finish pushing changes, pass all other checks, then paste a comment:

@jenkins-plone-org please run jobs

To ensure that these changes do not break other parts of Plone, the Plone test suite matrix needs to pass, but it takes 30-60 min. Other CI checks are usually much faster and the Plone Jenkins resources are limited, so when done pushing changes and all other checks pass either start all Jenkins PR jobs yourself, or simply add the comment above in this PR to start all the jobs automatically.

Happy hacking!

[Faakhir30]

@jenkins-plone-org please run jobs

[stevepiercy]

Hmm... the RTD preview build is still broken. I'll fiddle with its settings.