eKuiper 1.6.1 release

Overview

eKuiper 1.6.1 is a maintainance version that fixes several issues and add some properties to stabilize the product.
Most importantly, fix the instability connection issue with neuron, now neuron do not need to start before eKuiper.
For eKuiper cannot run directly in old linux distribution(ubuntu-18.04 centos-7) because of glibc compatibility issue,
now build eKuiper using old glibc. For the prebuilt native plugins, now they can run in alpine docker images. For documents, provide
protobuf tutorial, upload management api and correct outdated message.

Fixes

• Fix connecting to NanoMQ issue and use MQTT 3.1.1(4) when connect to MQTT broker by default @ngjaying
• Fix the invalid sink conf @ngjaying
• Use async connection with neuron @ngjaying
• Avoid chunked encoding for rest response @superrxan
• Add lock to toMap @ngjaying
• Remove strict check for plugin download @superrxan
• Fix restart may fail because the previous detach has not done issue @ngjaying
• Cache the Symbols when eKuiper starts up and plugins register @superrxan
• Fix the prebuilt plugins can not run on official build eKuiper binary issue @superrxan
• Fix the official build eKuiper binary can not run on lower linux distribution issue @superrxan

Feature

• Add alpine base build image and build alpine prebuilt plugins with it
• Connection exception management

Docs

• Provide protobuf tutorial
• Provide upload management api document
• Correct broken address reference
• Update go version to 1.18 in readme.md

New Contributors

• @sixhj made their first contribution in #1350
• @guowei-gong made their first contribution in #1363
• @MonicaisHer made their first contribution in #1375

Full Changelog: 1.6.0...1.6.1