Upgrade to ember 4.8.5

[elpoelma]

This PR includes an upgrade to ember-source 4.8.5 and ember-data 4.8.8.

Specifically it updates the following packages:

• ember source to 4.8.5 + related packages
• ember-data to 4.8.8
• @lblod/ember-mock-login to 0.7.0
• ember-drag-drop to 0.9.0-beta.0

Additionally, it removes the following obsolete packages:

• ember-load, an application-loading template is used instead
• ember-cached-decorator-polyfill, included in ember 4.8
• ember-functions-as-helper-polyfill, included in ember 4.8
• ember-unique-id-helper-polyfilll, included in ember 4.8

Additionally, this PR includes a fix which first awaits all participants of an agendapoint treatment, before loading them as voters.

[nvdk]

while not strictly necessary, I'd recommend upgrading the ember version in the docker file and woodpecker pipelines
( I'd suggest trying madnificent/ember:4.12.1-node_18 and danlynn/ember-cli:4.12.1-node_18.16)

[abeforgit]

tried all the flows I could think of, couldn't find anything else
good to go when CI passes