connectors-ci: fix pip install error

[alafanechere]

What

Closes #29147

Fixes two problems:

• with_exec("pip", "install", ...) was called too early: it was evaluated during the get_file_contents function, this function raised an unrelated errors because it first executed the lazy with_exec(["pip", "install"]) before processing the file content
• When a connector does not have a setup.py or requirements.txt using get_file_contents raises a dagger exception that we correctly handled but Dagger will still consider this as a failure on their UI when the file does not exist.

How

• Check if the file setup.py or requirements.txt exist with the check_path_in_workdir function. This function does not raise a Dagger exception if the file does not exist.
• Check if the file setup.py or requirements.txt exist before appending with_exec(["pip", "install", ...]) to the container: it solved the early raise of pip install error that led to sentry error capture

[octavia-squidington-iii]

source-intercom test report (commit 369002556b) - ❌

⏲️ Total pipeline duration: 01mn08s

Step	Result
Validate airbyte-integrations/connectors/source-intercom/metadata.yaml	✅
Connector version semver check	✅
QA checks	✅
Code format checks	✅
Connector package install	❌

🔗 View the logs here

☁️ View runs for commit in Dagger Cloud

Please note that tests are only run on PR ready for review. Please set your PR to draft mode to not flood the CI engine and upstream service on following commits.
You can run the same pipeline locally on this branch with the airbyte-ci tool with the following command

airbyte-ci connectors --name=source-intercom test

[octavia-squidington-iii]

source-openweather test report (commit 369002556b) - ✅

⏲️ Total pipeline duration: 02mn18s

Step	Result
Validate airbyte-integrations/connectors/source-openweather/metadata.yaml	✅
Connector version semver check	✅
QA checks	✅
Code format checks	✅
Connector package install	✅
Build source-openweather docker image for platform linux/x86_64	✅
Unit tests	✅
Acceptance tests	✅

🔗 View the logs here

☁️ View runs for commit in Dagger Cloud

Please note that tests are only run on PR ready for review. Please set your PR to draft mode to not flood the CI engine and upstream service on following commits.
You can run the same pipeline locally on this branch with the airbyte-ci tool with the following command

airbyte-ci connectors --name=source-openweather test

[alafanechere]

Manual testing

I triggered a test pipeline for source-intercom which is failing the pip install operation for unrelated reasons.
No new sentry event was sent for this error on this run: the pip install failure is correctly handled.