[BUG] - application inserts mimetype associations in user's mimeapps preferences instead of appending

[corigne]

Describe the bug
r2modman inserts its desktop file as the first entry in mimeapps.list for x-scheme-handler/https and others on start, even if another application already exists for this entry (e.g. firefox.desktop), ideally this should be appended to avoid overwriting existing user preferences

To Reproduce
Steps to reproduce the behavior:

1. Set default browser using mimeo or by hand
2. open an http link, default browser opens a new tab to that lnk
3. open r2modman
4. open the same http link, r2modman flashes briefly, nothing opens in the default browser

Expected behavior
r2modman should append, not insert mimeapps entries for mimetypoes that it doesn't explicitly own, respecting existing mimeapp preferences

Screenshots
n/a

Additional context
system info:
OS: Arch Linux x86_64
Kernel: Linux 6.9.4-arch1-1
WM: i3 (X11)
CPU: AMD Ryzen 7 3800X (16) @ 4.20 GHz
GPU: NVIDIA GeForce RTX 2070 SUPER [Discrete]
Locale: en_US.UTF-8