Update Watchtower version to 1.0.6

[o-nikolas]

Currently a pre 1.0 version of Watchtower is being used. There have been
many bug fixes and improvements since this version (the changelog can be found here).

This change updates Airflow's specified version in setup.py.

I have ran the following commands to test this locally:

./breeze generate-constraints --generate-constraints-mode source-providers

./scripts/ci/testing/ci_run_airflow_testing.sh

I believe this is the only line that needs to be changed for a dependency upgrade (see discussion I started on the community slack) but please correct me if I'm wrong here.

---

^ Add meaningful description above

Read the Pull Request Guidelines for more information.
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.

[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/main/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.
• Please follow ASF Code of Conduct for all communication including (but not limited to) comments on Pull Requests, Mailing list and Slack.
• Be sure to read the Airflow Coding style.
  Apache Airflow is a community-driven project and together we are making it better 🚀.
  In case of doubts contact the developers at:
  Mailing List: dev@airflow.apache.org
  Slack: https://s.apache.org/airflow-slack

[potiuk]

This one will fail likely . I looked at this and some recent change made "setup.py' changes do not work the way they should. Fix is coming #16470

[potiuk]

🤞

[boring-cyborg]

Awesome work, congrats on your first merged pull request!