Add custom "Holding" in investmen account

[Aohzan]

Describe the feature

Hello,
Currently it seems that if I want to manage transaction, I can only choose from Ticket symbol autocomplete field. If I'm not wrong, I would like to add custom line, and manage its value

Why is this feature important?

Synth doesn't provide all stocks values for example (french ETF in my case), and maybe it will allow to manage specific things like said in #1404

Additional context, screenshots, and relevant links

No response