Allow override of the path to oauth for impersonate user

[jeff-phillips-18]

Description

Fixes the URL path to oath when the dev server is running agains an RHOAI dashboard

How Has This Been Tested?

• For a cluster whose oath route is not oauth-openshift, Edit .env.local and set DEV_IMPERSONATE_USER and DEV_IMPERSONATE_PASSWORD to a valid combo and set DEV_OAUTH_PREFIX to the correct route.
• Run the dev server
• In the dev dashboard, select the user menu and Start impersonate
• Verify there are no errors and you now see only projects that DEV_IMPERSONATE_USER should see.

Test Impact

None, dev mode only

Request review criteria:

Self checklist (all need to be checked):

• The developer has manually tested the changes and verified that the changes work
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has added tests or explained why testing cannot be added (unit or cypress tests for related changes)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.76%. Comparing base (ebc2c66) to head (552ecf1).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3640      +/-   ##
==========================================
- Coverage   85.78%   85.76%   -0.02%     
==========================================
  Files        1419     1419              
  Lines       32684    32684              
  Branches     9191     9191              
==========================================
- Hits        28038    28033       -5     
- Misses       4646     4651       +5     

see 4 files with indirect coverage changes

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[christianvogt]

/lgtm
/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: christianvogt

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