[🚀 Feature]: use lowercase header names

[joerg1985]

Feature and motivation

I would suggest to convert all header names to lowercase in the HttpMessage.
It might be helpful in the future to have only lower case header names.

The header names should be in general treated case-insensitive, but there might be code somewhere not aware of this, so i would see this in Selenium 5.

Usage example

There is currently a hidden issue due to the case-sensitive map used in the HttpMessage.
The order of headers set depends currently on the map implementation and not on the order of adding them, this can be observed here:

selenium/java/test/org/openqa/selenium/remote/http/HttpMessageTest.java

Lines 53 to 57 in 938058d

	message.addHeader("Content-Length", "1024");
	message.addHeader("Content-length", "2048");
	message.addHeader("content-length", "4096");
	assertThat(message.getHeader("Content-Length")).isEqualTo("4096");

message.getHeader("Content-Length") should actually return "1024"

[github-actions]

@joerg1985, thank you for creating this issue. We will troubleshoot it as soon as we can.

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Thank you!

[diemol]

Makes sense to me.

[VAIBHAVPANT07]

assign me

[titusfortner]

We don't assign specific issues, but if you make a PR we'll happily review it. Thanks.

[manuelsblanco]

@diemol Is this still a issue? Can I take it?

[diemol]

@joerg1985 is this still pending?

[joerg1985]

@diemol yes this is still open, as it is in milestone selenium 5.0.
I think this could be implemented earlier, but there is a risk for e.g. appium to run into troubles.

[iampopovich]

@diemol @titusfortner What should we do with the HttpMessageTest class after the changes?
If the header names become case-insensitive, all tests will fail. Should we modify the logic of the existing tests or write new ones?