[FLINK-24509][docs] Add kafka serializer to producer examples

[alibahadirzeybek]

What is the purpose of the change

This pull request fixes documentation examples for the kafka producer by replacing the SimpleStringSchema with KafkaSerializationSchema

Brief change log

• A new KafkaSerializationSchema is created with basic topic and record content filling
• A newly created KafkaSerializationSchema is passed as the serialization schema to the FlinkKafkaProducer constructor

Verifying this change

This change does not affect any tests since it is an update to the documentation.

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

• Dependencies (does it add or upgrade a dependency): (no)
• 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)

[flinkbot]

CI report:

• b58e63c Azure: SUCCESS
• 124ffef Azure: PENDING

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[flinkbot]

Thanks a lot for your contribution to the Apache Flink project. I'm the @flinkbot. I help the community
to review your pull request. We will use this comment to track the progress of the review.

Automated Checks

Last check on commit b58e63c (Tue Oct 12 08:49:57 UTC 2021)

Warnings:

• Documentation files were touched, but no docs/content.zh/ files: Update Chinese documentation or file Jira ticket.

_{Mention the bot in a comment to re-run the automated checks.}

Review Progress

• ❓ 1. The [description] looks good.
• ❓ 2. There is [consensus] that the contribution should go into to Flink.
• ❓ 3. Needs [attention] from.
• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

Please see the Pull Request Review Guide for a full explanation of the review process.

The Bot is tracking the review progress through labels. Labels are applied according to the order of the review items. For consensus, approval by a Flink committer of PMC member is required

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot approve description to approve one or more aspects (aspects: description, consensus, architecture and quality)
• @flinkbot approve all to approve all aspects
• @flinkbot approve-until architecture to approve everything until architecture
• @flinkbot attention @username1 [@username2 ..] to require somebody's attention
• @flinkbot disapprove architecture to remove an approval you gave earlier

[alpinegizmo]

LGTM. @alibahadirzeybek Can you rebase this on release-1.13 please?

[alibahadirzeybek]

LGTM. @alibahadirzeybek Can you rebase this on release-1.13 please?

Done