Add gh Actions cron job to approve new member requests on Spond

[pavelskipenes]

Getting information about a group (including membership requests): GET https://spond.com/api/2.1/group/GROUP_ID
Approving membership requests: POST https://spond.com/api/2.1/group/GROUP_ID/membershipRequest/REQUEST_ID/approve
API endpoint needs authentication. Create a new bot user to the group as admin.

Spond API is not documented so here are other implementations for reference:

• https://github.com/Olen/Spond
• https://github.com/Horten-Folkeverksted/hortenfv-member-import

[pavelskipenes]

POST https://spond.com/api/2.1/group/GROUP_ID/members with payload:

[
    {
        "id":"USER_ID",
        "subGroups": [
            "SUBGROUP_ID",
            "SUBGROUP_ID"
        ]
    }
]

constants for this project / note to self:

GROUP_ID: 683683854E1E4A24ACE812F439363128
SUBGROUP_ID:
Arrangement: 7964AB3FB59F45D2AFB6DD546A8EFE50
Medlemmer 2022: A16BF00C60C743C0A72F1AE818896189