PushRegistrationManager: fix repeated sending of requests

[rfc2822]

See bitfireAT/dav4jvm#156 first

Purpose

This PR updates the PushRegistrationManager to use TextContent instead of ByteReadChannel for POST requests, addressing issue #2073.

Short description

• Replaced ByteReadChannel with TextContent in PushRegistrationManager.
• Updated the bitfire-dav4jvm dependency to commit 30472e34d6.

Note: dav4jvm commit ID will be updated to latest main before merging.

Checklist

• The PR has a proper title, description and label.
• I have self-reviewed the PR.
• I have added documentation to complex functions and functions that can be used by other modules.
• I have added reasonable tests or consciously decided to not add tests.

[ArnyminerZ]

I don't fully 100% understand why this fixes the issue, but makes sense I guess. Feel free to merge.

[rfc2822]

I don't fully 100% understand why this fixes the issue, but makes sense I guess. Feel free to merge.

👍🏻 In short:

content = { ByteReadChannel(writer.toString()) } only looks as if it would create a ByteReadChannel for every request, but actually dav4jvm calls the content() and then feeds a single ByteReadChannel to Ktor. And by definition, ByteReadChannels are one-shot, so they only work if Ktor is sending only one request.

As soon as it has to repeat the request for whatever reason (authentication required, redirect, retry on timeout, whatever), it sends an empty request instead (because the ByteReadChannel is already consumed).

Using OutgoingContent guarantees that everything is as needed by Ktor.