Add login redirect

[nknguyenhc]

Summary:

Fixes #1229

Changes Made:

• Allow the application to redirect to next route if any.
• Checks if the next route is allowed before redirecting to it.
• Stores the next route in session storage.

Unlike CATcher-org/WATcher#255,

• Routes are already changed when each view changes. This PR simply aims to redirect to the target route after logging in.
• This is meant to work with any phase.

Note that it only redirects to the current phase. If there are multiple open phases, the app only allows redirection to the "current phase", which is the first available phase. However, given that in CATcher, only one phase is allowed at a time,

Proposed Commit Message:

Add login redirect

Previously, upon login, users are brought to the
default landing page of the phase.

We redirect to the intended landing page,
with appropriate next route checking.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 9.09091% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 54.62%. Comparing base (5e7ed48) to head (951e632).

Files	Patch %	Lines
src/app/core/services/auth.service.ts	9.09%	9 Missing and 1 partial :warning:

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1256 +/- ## ========================================== - Coverage 54.82% 54.62% -0.21% ========================================== Files 105 105 Lines 2858 2867 +9 Branches 503 504 +1 ========================================== - Hits 1567 1566 -1 - Misses 1030 1038 +8 - Partials 261 263 +2 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[luminousleek]

Using an invalid URL (e.g. linking to an issue that doesn't exist) should redirect to the default landing page, but currently displays a blank page.

[nknguyenhc]

Using an invalid URL (e.g. linking to an issue that doesn't exist) should redirect to the default landing page, but currently displays a blank page.

Fixed! In ViewIssueComponent::getAndPollIssue, I redirect to current phase landing page if there is error polling the issue.

[luminousleek]

Fixed! In ViewIssueComponent::getAndPollIssue, I redirect to current phase landing page if there is error polling the issue.

Cool, is it possible to have an error popup when this happens?