Change portfolio mode to use custom sort order

[Airiinnn]

What feature(s) would you like to see in RepoSense

Now that custom sort order (follows initial order of rows in repo-config.csv) has been added in #2331, it would be better for portfolio mode to use that ordering instead of the current sort by ascending group name.

Reasoning is that there is currently no way for the user (portfolio creator) to specify the order of the repositories in portfolio mode. It would be better for the user to be able to customize the order through the config file, so they can put more important / recent projects at the top.

Is the feature request related to a problem?

If possible, describe the solution

For portfolio mode, change the filter settings when filtering repositories to use the custom sort order.

It should be a small change in c-summary-portfolio.vue (as well as tests).

If applicable, describe alternatives you've considered

Additional context