[FLINK-39857] Upgrade Pekko to 1.6.0

[snuyanzin]

What is the purpose of the change

The PR bumps Pekko to 1.6.0 (tested against java25 and scala2.12.21 in Pekko's ci)

Brief change log

pom, NOTICE

Verifying this change

existing tests

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes )
• The public API, i.e., is any changed class annotated with @Public(Evolving): ( no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: ( no)

Documentation

• Does this pull request introduce a new feature? ( no)
• If yes, how is the feature documented? (not applicable)

---

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

[flinkbot]

CI report:

• 9f5d6ec Azure: SUCCESS

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[jnh5y]

From the release notes https://pekko.apache.org/docs/pekko/current/release-notes/releases-1.5.html and https://pekko.apache.org/docs/pekko/current/release-notes/releases-1.6.html, 1.6 is trivial.

1.5 does change some dependencies:

netty 4.2.10.Final
jackson 2.21.2
protobuf-java 4.33.5
config 1.4.6
lz4-java 1.10.4

I have two concerns:

typesafe config 1.4.2 -> 1.4.6: Currently pinned to 1.4.2 in flink-rpc/flink-rpc-akka/pom.xml:143. Pekko 1.6 likely requires 1.4.6

protobuf-java 4.33.5 Looks like the protoc.version is 4.32.1 and may be used to managed protobuf-java elsewhere.

Do we need to think through that? Maybe relocate this version in the flink-rpc-akka module?

[snuyanzin]

look at ./mvnw dependency:tree for flink-rpc-akka

INFO] +- org.apache.pekko:pekko-actor_2.12:jar:1.6.0:compile (optional) 
[INFO] |  +- org.scala-lang:scala-library:jar:2.12.21:compile (optional) 
[INFO] |  +- org.scala-lang.modules:scala-java8-compat_2.12:jar:1.0.2:compile (optional) 
[INFO] |  \- com.typesafe:config:jar:1.4.2:compile (optional) 
[INFO] +- org.apache.pekko:pekko-remote_2.12:jar:1.6.0:compile (optional) 
[INFO] |  +- org.apache.pekko:pekko-stream_2.12:jar:1.6.0:compile (optional) 
[INFO] |  |  +- org.apache.pekko:pekko-protobuf-v3_2.12:jar:1.6.0:compile (optional) 
[INFO] |  |  +- org.reactivestreams:reactive-streams:jar:1.0.4:compile (optional) 
[INFO] |  |  \- com.typesafe:ssl-config-core_2.12:jar:0.7.1:compile (optional) 
[INFO] |  +- org.apache.pekko:pekko-pki_2.12:jar:1.6.0:compile (optional) 
[INFO] |  |  \- com.hierynomus:asn-one:jar:0.6.0:compile (optional) 
[INFO] |  \- org.agrona:agrona:jar:1.22.0:compile (optional) 
[INFO] +- org.apache.pekko:pekko-slf4j_2.12:jar:1.6.0:compile (optional) 

[snuyanzin]

we don't use pekko's protobuf v4
instead we use v3
updated config

[jnh5y]

Looks good; thanks for updating the typesafe config.