URL encode execution date in the Last Run link

[alexbegg]

closes: #10434

The problem is when execution_date is passed in the URL unencoded for the "Last Run" link it results in an incorrect pendulum datetime when pendulum.parse() is used in the codebase. The time of the pendulum datetime gets incorrectly returned as 00:00:00 no matter what time the execution date has. URL encoding the execution_date value fixes the problem.

This was already fixed in all other places execution_date is used in URLs years ago with commit 9ec7f0f, but Last Run is more recent so this was missed.

---

^ 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/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.
• 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: [email protected]
  Slack: https://apache-airflow-slack.herokuapp.com/

[boring-cyborg]

Awesome work, congrats on your first merged pull request!