Add ServerMetrics to collect metrics related server

[seongbeenkim]

Motivation:

Add ServerMetrics to collect metrics related server. #4992

Modifications:

• Add ServerMetrics.increasePendingHttp1Requests() in Http1RequestDecoder#channelRead before fireChannelRead()
• Add ServerMetrics.increasePendingHttp2Requests() in Http2RequestDecoder#onHeadersRead before fireChannelRead()
• Add ServerMetrics.decreasePendingHttp1Requests(), ServerMetrics.decreasePendingHttp2Requests(), ServerMetrics.increaseActiveHttp1WebSocketRequests(), ServerMetrics.increaseActiveHttp1Requests() and ServerMetrics.increaseActiveHttp2Requests() in HttpServerHandler#serve0 before service.serve(reqCtx, req)
• Add ServerMetrics.decreaseActiveHttp1WebSocketRequests(), ServerMetrics.decreaseActiveHttp1Requests() and ServerMetrics.decreaseActiveHttp2Requests() in AbstractHttpResponseHandler#tryComplete
• Add ServerMetrics.increaseActiveConnectionsAndGet() and ServerMetrics.decreaseActiveConnections() in ConnectionLimitingHandler#channelRead

Result:

• Closes #4992. (If this resolves the issue.)
• users can implement features based on ServerMertrics like graceful shutdowns such as stopping the server when there are no pending requests.

[CLAassistant]

All committers have signed the CLA.

[github-actions[bot]]

🔍 Build Scan® (commit: 9371f15c6ceb647890230bbc6f337710e713c68d)

Job name	Status	Build Scan®
build-windows-latest-jdk-21	✅	https://ge.armeria.dev/s/f6dangr2eafsq
build-self-hosted-unsafe-jdk-8	✅	https://ge.armeria.dev/s/jgktuyts66nym
build-self-hosted-unsafe-jdk-21-snapshot-blockhound	✅	https://ge.armeria.dev/s/trchnvzvvczmq
build-self-hosted-unsafe-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/nnvlgviplsawm
build-self-hosted-unsafe-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/y6fsk52tlpdm4
build-self-hosted-unsafe-jdk-17-leak	✅	https://ge.armeria.dev/s/tg552oevoqtns
build-self-hosted-unsafe-jdk-11	✅	https://ge.armeria.dev/s/ppsia33yhdrvi
build-macos-12-jdk-21	✅	https://ge.armeria.dev/s/3ir4tnr5aqgho

[minwoox]

Let me resolve the conflict. 😉

[jrhee17]

Gentle ping 🙏

[minwoox]

I've pushed commits because we are about to release the next version. There are also some failing tests that will be resolved after https://github.com/line/armeria/pull/5680 gets merged.

[minwoox]

Thanks a lot, @seongbeenkim! 😉