add an option to disconnect from a route that needs upstream oauth (#121)

if a route needs an upstream oauth, sometimes the user needs to purge
its upstream authentication so that it can re-acquire it again, possibly
with different scopes and options.

adds a ui component that allows to do that. 
<img width="393" alt="image"
src="https://github.com/user-attachments/assets/cc136b2d-4a4f-4f5a-bd21-04099ecef838"
/>

Ref:
https://linear.app/pomerium/issue/ENG-2545/mcp-user-should-be-able-to-purge-their-upstream-oauth2-token

Depends on: pomerium/pomerium#5707

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Co-authored-by: Nick Taylor <nick@nickyt.co>

Author: wasaga