[Meta] Support JDK16/17

[andsel]

JDK 16 is actually in "early-access" but is expected to be GA on 2021/03/16 https://openjdk.java.net/projects/jdk/16/
It brings:

• JEP 390: deprecates native types wrapper constructors, so no more new Long(n). Logstash doesn't use these but JRuby seems to use it https://github.com/jruby/jruby/blob/48208dcb1e750013869c6f627350d4a420201adb/core/src/main/java/org/jruby/parser/RubyParser.java#L3864 and I'm not able to view if this could impact Logstash
• JEP 386: Alpine Linux support, since the Alpine uses another libc we should try to run against it
• JEP 396: Strongly Encapsulate JDK Internals by Default, we could crash against modules, not directly but for some libraries Logstash use.
• JEP 388: Windows/AArch64 Port, this probably worth an eye

According to JEPs list in JDK 17 https://openjdk.java.net/projects/jdk/17/ we could crash against:

• JEP 411 Deprecate the Security Manager for Removal this means java.security.AccessController usage has to be reworked
• JEP 403 Strongly Encapsulate JDK Internals internal classes like sun.misc.Unsafe are not anymore usable, which could maybe lead us to update some dependencies.

JDK 16 Task list

• run the build with openJDK16 Update CI to run on AdoptOpenJDK16 #13202
• update CI to use JDK16 https://github.com/elastic/infra/pull/31324
• run Logstash package with JDK 16 on Alpine Linux
  • use Dockerfile.alpine https://gist.github.com/andsel/38972519c366a673f7d4487e7eaa2695
  • clone the Fix failing test under JDK16 #13203 branch https://github.com/andsel/logstash/tree/fix/jdk16_adaptations
  • bring the Dockerfile.alpine into the local clone
  • build the image docker build -t logstash_alpine . -f Dockerfile.alpine
  • build the packages rake artifact:archives
  • run a shell in the image mounting the build/ folder with docker run --rm -it -v `pwd`/build:/opt/logstash/build logstash_alpine sh
  • unpack the previously created Logstash tar.gz package: in the image shell run cd /opt/logstash/build/ and tar zxf logstash-8.0.0-SNAPSHOT-no-jdk.tar.gz
  • run logstash sh bin/logstash -e "input {stdin{}} output{stdout{codec => rubydebug}}"
• fixes for the build Fix failing test under JDK16 #13203
• verify mostly used plugins works with JDK 16

JDK 17 Task list

• run the build with openJDK17 Update JDK matrix to include JDK17: OpenJDK, AdoptiumJDK and Zulu #13307
• update CI to use JDK 17 https://github.com/elastic/infra/pull/32212
• run LS with JDK 17 on Alpine Linux
  • verified using https://gist.github.com/robbavey/ad4cdf044ab8237a9bc4f23883f86e50
• remove usage of Security Manager Fixes to build and run Logstah on JDK 17 #13306
• eventually update any dependency that still use the removed sun.misc.Unsafe class
• bundle AdomptiumOpenJDK 17 into 8.0 PR Update bundled JDK to jdk 17 #13343
• verify tier1 and tier2 plugins works with JDK 17
• configure G1GC flags appropriately for JDK 17 (the default GC of the JVM) Determine best G1GC flags to avoid too much compromise on performance and memory consumption #13378
• update plugins Gradle wrapper version to a JDK 17 compatible (Gradle >= 7)
  • Azure EventHub input Fix build script to run with Gradle 7 logstash-plugins/logstash-input-azure_event_hubs#69
  • Beats input Fix build script to run with Gradle 7 logstash-plugins/logstash-input-beats#432
  • File input Update to Gradle 7.2 logstash-plugins/logstash-input-file#305
  • Http Input Fix build script to run with Gradle 7 logstash-plugins/logstash-input-http#145
  • Kafka integration (input and output) Fix build script to run with Gradle 7 logstash-plugins/logstash-integration-kafka#104
  • TCP input Fix build script to run with Gradle 7 logstash-plugins/logstash-input-tcp#184
  • Date filter Fix build script to run with Gradle 7 logstash-plugins/logstash-filter-date#140
  • Geoip filter Fix build script to run with Gradle 7 logstash-plugins/logstash-filter-geoip#191
  • User agent filter Fix build script to run with Gradle 7 logstash-plugins/logstash-filter-useragent#75
  • SNMP input (Tier 2) Fix build script to run with Gradle 7 logstash-plugins/logstash-input-snmp#102
  • Dissect filter Fix build script to run with Gradle 7 logstash-plugins/logstash-filter-dissect#78