Migrate from `vue-multiselect` to `vueform/multiselect`

[mrleblanc101]

vueform/multiselect is better maintained and has better accessibility.
Both have very similar API, so it's shouldn't be too much of a hassle to migrate.
Another benefit is that vueform/multiselect support appending the dropdown to the body which would prevent the dropdown from being cut when they are placed inside a modal: vueform/multiselect#341

[mrleblanc101]

Here is a complete comparaison: https://github.com/vueform/multiselect?tab=readme-ov-file#comparison-with-other-libraries