Fix e2e regression caused by changes in AuthService

[cheehongw]

Summary:

Fixes #1274

Changes Made:

Added missing method signatures in MockAuthService so that it exists and can be called when the application is running in a test environment such as Playwright. They are:

• navigateToLandingPage
• clearNext
• storeNext
• getNext

It is also the reason why our Playwright tests are failing - the test environment crashes when it runs into the new method signatures that are not defined in MockAuthService.

Proposed Commit Message:

Fix e2e regression caused by changes in AuthService

Previously, a PR introduced new method signatures in AuthService.
However, these were not introduced in MockAuthService, causing 
the testing environment to fail when the application encountered these
undefined method signatures.

Lets address this regression by adding the method signatures for these
methods.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 58.84%. Comparing base (5e7ed48) to head (955b20a). Report is 8 commits behind head on master.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1275 +/- ## ========================================== + Coverage 54.82% 58.84% +4.01% ========================================== Files 105 105 Lines 2858 2573 -285 Branches 503 289 -214 ========================================== - Hits 1567 1514 -53 + Misses 1030 1009 -21 + Partials 261 50 -211 ```

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