Provide way to change context (package / top-level) in Web UI

[isc-tleavitt]

Use case:
IRIS BI editors - specifically the user portal - are misbehaving and not launching the web UI for some reason. (The page just reloads.)* As a workaround, I should be able to go back to the home page and get to the Git WebUI for my own package (or the top-l;evel repo for the namespace).

If the Web UI is launched without a context, it should help the user select one based on valid configuration: top level (if namespace temp folder has .git) and any git-configured packages. It should also be possible to change context after the fact.

*I don't know what the cause is, that's a separate issue (encountered in my development environment for a personal side project). $zv is IRIS for Windows (x86-64) 2022.3 (Build 606U) Mon Jan 30 2023 09:12:22 EST.

[isc-tleavitt]

@isc-tleavitt to provide a class query that works for IPM 0.7.x and 0.9.0 to do the right things here - we need to get, given a namespace, all the names of packages that were loaded from git repos. (That is, they're in DeveloperMode and have a .git folder under the package Root folder.)

@isc-hwojnick to do the UI