Refactor connection creation in system tests to use REST API instead

[ramitkataria]

Since direct DB access is not permitted in Airflow 3 due to Task SDK, the these system tests were failing during connection creation when run with Task SDK. This refactors the tests so they use REST API to create the connection.

Also added a helper method to make REST API calls for tests without having to manually create the request.

I've tested the create_connection task and confirmed it does create the connection.

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an 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 a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[potiuk]

We might eventually replace it with with python client - but I think it's good enough for now cc: @VladaZakharova @kosteev ?

[potiuk]

BTW. The errors are unrelated - one of them random, one of them being fixed in main.

[ramitkataria]

Hi @potiuk

BTW. The errors are unrelated - one of them random, one of them being fixed in main.

Is error occurring right now the one being fixed in main? Otherwise I was thinking of moving the import statement to be inside the function

[potiuk]

@ramitkataria -> Generelly when in doubt - rebase and check if it still fails. Always Be Rebased is the motto you should use. That helps to see if the issue is resolved without involving maintainers - they migth or might not know about some current or even new failures. You are 20 commits behind already.