fix(MeshHttpRoute): don't split header value prematurely

[spacewander]

Fix #10156
Signed-off-by: spacewander spacewanderlzx@gmail.com

Checklist prior to review

• #10156 as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
  • Don't forget ci/ labels to run additional/fewer tests
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? (this GH action will add "backport" label based on these file globs, if you want to prevent it from adding the "backport" label use no-backport-autolabel label) --

[spacewander]

Will fix the unit test later.

[slonka]

from the issue:

I think Envoy will do the right thing here, we should change this.

@michaelbeaumont did you by any chance had time to check if it does the right thing?

[michaelbeaumont]

LGTM, thanks @spacewander !