Adds XMLRPCRequest missing accept header

[antonis]

Fixes wordpress-mobile/WordPress-Android#7846

Description

This PR adds the Accept: */* header to:

• aAll XMLRPC Requests 2b4718b
• the media upload request 115f8b7

This aligns with the behaviour of the iOS app wordpress-mobile/WordPress-Android#7846 (comment)

To test

1. Use the WPAndroid app from Adds XMLRPCRequest missing accept header WordPress-Android#19683
2. Setup a proxy to observe the network traffic
3. Login to a self-hosted site. You can use JN to create an ephemeral self hosted site an use the Add self-hosted site option from the site chooser > add(+) menu.
4. Create a Post, write a comment etc
5. Add an image from the device
6. Verify that all the network requests have the Accept: */* header.

[justtwago]

The code looks good! I'm unable to test it since I have difficulties with setting up a test self-hosted site. I'm approving the PR not to block it since it's a straightforward change, but feel free to wait for another review if you wish.

[justtwago]

Tested it on a Jurassic Ninja-based self-hosted site and it works as expected: I can see the accept: */* header. 🚀

[antonis]

Thank you for reviewing and testing @justtwago 🙇