chore: change Namespace enum to stirng

[yeager-eren]

Summary

Using a single source of truth for Namespace.

We need to use a single type for both legacy and hub implementation. To make it more general and don't needing to always keeping the namespace updated by what Rango currently support, I changed it to string, instead of enum. To have namespace suggestion while coding, I used a trick to suggest our supported namespaces alongside the fact that it can be any string.

Fixes # (issue)

How did you test this change?

It should be compiled correctly, shouldn't affect the functionality of working with wallets.

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• Implemented a user interface (UI) change, referencing our Figma design to ensure pixel-perfect precision.

[nikaaru]

LGTM