fix(outputs.opentelemetry): Prevent goroutine leak on gzip write failure

[skartikey]

Summary

Close the gzip pipe reader returned by CompressWithGzip in Export.
If the HTTP request fails or the server responds before consuming the full body, the gzip goroutine can block on PipeWriter.Write, causing a memory leak.

While reviewing #18416 (which fixed this in outputs.influxdb), I checked other CompressWithGzip call sites. outputs.opentelemetry was the only remaining caller missing the close. Other plugins (outputs.http, outputs.sensu, outputs.loki) already use defer rc.Close().

Related to #18413, #18416

Checklist

• No AI generated code was used in this PR
• AI generated code used in this PR follows the InfluxData Policy on AI-Generated Code Contributions

Related issues

resolves #

[srebhan]

@skartikey I agree with @Hipska's comment, please directly assign to reader.

[telegraf-tiger]

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. DEB	. RPM	. TAR . GZ	. ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	darwin_arm64.tar.gz	windows_arm64.zip
armel.deb	armv6hl.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armhf.deb	i386.rpm	freebsd_armv7.tar.gz
i386.deb	ppc64le.rpm	freebsd_i386.tar.gz
mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
		linux_s390x.tar.gz