This patch moves the initialisation of a HTTP/1.1 stream from the
session initialisation to the session ingestion step.

Previously, using keep-alive on HTTP/1.1 would panic on the second
request, as it would attempt to use components like the header map that
are destroyed after each stream, but only initialised at the start of
the session, when the HTTP protocol autodetection was run.

Signed-off-by: Andrew Titmuss <iandrewt@icloud.com>

This patch stops the forced connection-close for requests that aren't
HTTP/2 on the in_http plugin

Signed-off-by: Andrew Titmuss <iandrewt@icloud.com>

This patch stops the forced connection-close for requests that aren't
HTTP/2 on the in_elasticsearch plugin

Signed-off-by: Andrew Titmuss <iandrewt@icloud.com>

This patch stops the forced connection-close for requests that aren't
HTTP/2 on the in_opentelemetry plugin

Signed-off-by: Andrew Titmuss <iandrewt@icloud.com>

This patch stops the forced connection-close for requests that aren't
HTTP/2 on the in_splunk plugin

Signed-off-by: Andrew Titmuss <iandrewt@icloud.com>

This patch addresses feedback from @leonardo-albertovich, reducing how
many components are being recreated on each new request for a single
session. Now it only recreates the request object, rather than creating
a new stream for each request of a session.

It replaces my original fix in 0ef074a

Signed-off-by: Andrew Titmuss <iandrewt@icloud.com>

Signed-off-by: Andrew Titmuss <iandrewt@icloud.com>