Core: Fluent Bit's http server does not respond when enabling keepalive and failed to upgrade to HTTP/2

[cosmo0920]

Bug Report

Describe the bug

When failed to upgrade HTTP/2 from HTTP/1.1 with http2 true in input plugins, enabling keepalive is harmful because HTTP response does not happen and stale.
This behavior causes this #9010 type of issues.
Meanwhile, we need to disable keepalive on internal of http server

In this PR #9019, we actually disable keepalive automatically when HTTP/2 upgrade is failed.

Expected behavior

When enabling keepalive, the HTTP response should be returned to callee.

Screenshots

Your Environment

• Version used:
• Configuration:
• Environment name and version (e.g. Kubernetes? What version?):
• Server type and version:
• Operating System and version:
• Filters and plugins:

Additional context

[edsiper]

fixed in #9036