#1658 api: JWT with RS256

[SamuelPull]

Checklist

• [x] I have followed (at least) the PR section of the contributing guide.
• [x] I fixed all necessary PR warnings
• [x] The commit history is clean
• [x] The E2E tests are passing
• [x] If possible, the issue has been divided into more subtasks
• [x] I did a self review before requesting a review from another team member

Some other services also use JWT_SECRET in certain scenarios. Check if there are further changes needed.

• [x] email-notification-service (doesn't work with authentication turned on, see https://github.com/openkfw/TruBudget/issues/1769
• [x] excel-export-service
• [ ] blockchain (connects to email service) - not working on m2 machine, can't fix

Description

How to test

1. Set new env vars: JWT_ALGORITHM=RS256, JWT_SECRET=base 64 pem encoded private key, JWT_PUBLIC_KEY=base 64 pem encoded public key
2. log in
3. token cookie should be RS256
4. do some stuff
5. old configuration should work too (no JWT_ALGORITH, or set to HS256, no public key, whatever secret)

Closes #1658

[github-actions[bot]]

	Warnings
:warning:	No CHANGELOG added.

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[openkfwCI]

	Notes	Time
:white_check_mark:	Note for Reviewer: E2E tests on pipeline 58500 on remote server succeeded	Fri, 12 Apr 2024 07:15:27 +0000

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