feat: add callback to accept auth tokens as part of VSC login

[heyzec]

Description

FYP: Source Academy as Visual Studio Code Extension

This is a minor change to add a new route /login/vscode_callback, which is a variant of /login/callback. It saves auth tokens into the Redux store after obtaining it via an exchange with a temp token.

See source-academy/backend#1240

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Code quality improvements

How to test

Checklist

• I have tested this code
• I have updated the documentation

[coveralls]

Pull Request Test Coverage Report for Build 14174579916

Details

• 1 of 15 (6.67%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 31.104%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/pages/login/LoginVscodeCallback.tsx	0	14	0.0%

Totals
Change from base Build 14054407863:	-0.02%
Covered Lines:	4888
Relevant Lines:	14823

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💛 - Coveralls

[RichDom2185]

LGTM, thanks!