Amazon S3: Mismatch when reading HTTP header from GCS

[gouyelliot]

This commit includes the HTTP separator when looking for the header values in the response payload, to avoid mismatching header ending with the same name. See the linked issue for more info and example.

Fixes #8790

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

[vg-meesho]

Hey @PettitWesley, can we get this PR reviewed and merged? Currently, there is no GCS Output Plugin but this fix could help as a workaround to upload to GCS bucket meanwhile.

[vg-meesho]

@PettitWesley @sparrc @singholt @swapneils

Bumping up for review