ADX-1062 Default to "member" role for new requests

[jonathansberry]

Description

Small change to ensure that the default value when selecting a role to join an organisation is member.

Also casts the return of the helper get_member_request_list from a FilterObject to a list because an empty FilterObject does not evaluate to False which is why the membership requests table shows in the front end even if there are no membership requests. .

Checklist

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• The Jira ticket for this issue has been updated to "Ready to Review" or equivalent.
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