Update the releasing-files section

[rebkwok]

• moves releasing docs to a subfolder and updates relevant links
• Splits out the information about requesting release of files (allowed filetypes, advisory notes to request when final etc) from instructions on the process itself
• Links to Airlock docs as the primary process for requesting release
• Moves the old process to a secondary page (still linked, but noted as deprecated)
• Some updates to the overview page
• Removes the section on viewing unreleased outputs from the job-server page, and replaces with a link to Airlock docs

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[rebkwok]

@bloodearnest Thanks - I'm going to merge this as is now, but will look at the new section this week, I think that's a good idea