[AIRFLOW-6830] Add Subject/MessageAttributes to SNS hook and operator

[snazzyfox]

Add subject and message_attributes as possible parameters for AwsSnsHook and SnsPublishOperator. Both defaults to none and are backwards compatible.

---

Issue link: AIRFLOW-6830

Make sure to mark the boxes below before creating PR: [x]

• Description above provides context of the change
• Commit message/PR title starts with [AIRFLOW-NNNN]. AIRFLOW-NNNN = JIRA ID^*
• Unit tests coverage for changes (not needed for documentation changes)
• Commits follow "How to write a good git commit message"
• Relevant documentation is updated including usage instructions.
• I will engage committers as explained in Contribution Workflow Example.

^* For document-only changes commit message can start with [AIRFLOW-XXXX].

---

In case of fundamental code change, Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in UPDATING.md.
Read the Pull Request Guidelines for more information.

[boring-cyborg]

Congratulations on your first Pull Request and welcome to the Apache Airflow community! If you have any issues or are unsure about any anything please check our Contribution Guide (https://github.com/apache/airflow/blob/master/CONTRIBUTING.rst)
Here are some useful points:

• Pay attention to the quality of your code (flake8, pylint and type annotations). Our pre-commits will help you with that.
• In case of a new feature add useful documentation (in docstrings or in docs/ directory). Adding a new operator? Check this short guide Consider adding an example DAG that shows how users should use it.
• Consider using Breeze environment for testing locally, it’s a heavy docker but it ships with a working Airflow and a lot of integrations.
• Be patient and persistent. It might take some time to get a review or get the final approval from Committers.
  Apache Airflow is a community-driven project and together we are making it better 🚀.
  In case of doubts contact the developers at:
  Mailing List: [email protected]
  Slack: https://apache-airflow-slack.herokuapp.com/

[codecov-io]

Codecov Report

Merging #7451 into master will decrease coverage by 0.28%.
The diff coverage is 95%.

@@            Coverage Diff             @@
##           master    #7451      +/-   ##
==========================================
- Coverage   86.66%   86.37%   -0.29%     
==========================================
  Files         877      877              
  Lines       41241    41266      +25     
==========================================
- Hits        35742    35645      -97     
- Misses       5499     5621     +122

Impacted Files	Coverage Δ
airflow/providers/amazon/aws/operators/sns.py	100% <100%> (ø)	⬆️
airflow/providers/amazon/aws/hooks/sns.py	96.42% <94.11%> (-3.58%)	⬇️
airflow/kubernetes/volume_mount.py	44.44% <0%> (-55.56%)	⬇️
airflow/kubernetes/volume.py	52.94% <0%> (-47.06%)	⬇️
airflow/kubernetes/pod_launcher.py	47.18% <0%> (-45.08%)	⬇️
...viders/cncf/kubernetes/operators/kubernetes_pod.py	69.38% <0%> (-25.52%)	⬇️
airflow/kubernetes/refresh_config.py	50.98% <0%> (-23.53%)	⬇️
airflow/configuration.py	87.78% <0%> (-0.23%)	⬇️
airflow/config_templates/default_celery.py	52.94% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update dbcd3d8...3ee2f6b. Read the comment docs.

[feluelle]

Some minor issues I overlooked.

[boring-cyborg]

Awesome work, congrats on your first merged pull request!

[feluelle]

@snazzyfox Thank you very much :) 👍