Define custom portfolios and use in Doc Builder

It'd be useful to have an area in Plannr where we're able to centrally define custom Portfolios (including name of Portfolio, names of individual funds included, allocation percentages etc).
We could then assign each client's plan to a Portfolio, and there could also be data placeholders for Document Builder, so that portfolio details can be dynamically inserted into documents.

The current function for Portfolios in Plannr is very limited and not very useful in my opinion, as it only assigns a portfolio name.

Ideally this would be a space within Settings, where an admin can go to set up their firm's portfolios and define the holdings for each portfolio.