fix: Pass headers for GET and DELETE requests

[usame-algan]

What it solves

We are using fetchData for POST, PUT and GET requests and have some logic in there to only set headers if there is a body. With the new endpoints added in #148 GET and DELETE requests now also contain headers so this doesn't work anymore.

How it is solved

• Adds a new util function called getData
• Partially reverts changes to fetchData done in feat: register, change and verify email addresses #148
• Passes headers to deleteData

I've also written more unit tests to cover these cases.

[github-actions]

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Type	Occurrences	Fixable
Errors	0	0
Warnings	0	0
Ignored	0	N/A

• Result: ✅ success
• Annotations: 0 total

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