[Mailer] Update Infobip API transport

[ndousson]

Q	A
Branch?	6.2
Bug fix?	yes
New feature?	no
Deprecations?	no
Tickets	N/A
License	MIT
Doc PR	N/A

📍 Context

Infobip send an email to their customers that do not use the latest API release: V3

They inform that everything is backward compatible and can be easily upgraded without any changes.

🛠️ Changes

This PR change the version used from the V2 to the V3.

[carsonbot]

Hey!

To help keep things organized, we don't allow "Draft" pull requests. Could you please click the "ready for review" button or close this PR and open a new one when you are done?

Note that a pull request does not have to be "perfect" or "ready for merge" when you first open it. We just want it to be ready for a first review.

Cheers!

Carsonbot

[carsonbot]

Hey!

I see that this is your first PR. That is great! Welcome!

Symfony has a contribution guide which I suggest you to read.

In short:

• Always add tests
• Keep backward compatibility (see https://symfony.com/bc).
• Bug fixes must be submitted against the lowest maintained branch where they apply (see https://symfony.com/releases)
• Features and deprecations must be submitted against the 6.3 branch.

Review the GitHub status checks of your pull request and try to solve the reported issues. If some tests are failing, try to see if they are failing because of this change.

When two Symfony core team members approve this change, it will be merged and you will become an official Symfony contributor!
If this PR is merged in a lower version branch, it will be merged up to all maintained branches within a few days.

I am going to sit back now and wait for the reviews.

Cheers!

Carsonbot

[nicolas-grekas]

Can you please split this PR in two?
One for 6.2, that just bump the number in the default endpoint. This will be a bugfix and doesn't need any change to the CHANGELOG file

Another one for 6.3 to propose the new attributes. Note that no other bridges support similar features and we've been super careful not to create bridges with too custom behaviors. This might be discussed on that new PR.

[ndousson]

Thanks Nicolas for your feedback 🙏

I'll split this PR as you suggest.

I know that other bridges didn't work like Infobip but I hope we'll find a good way to be able to use reporting behavior 👍
We'll see in the PR for 6.3

[nicolas-grekas]

Thank you @ndousson.