Implement passing dotenv variables to bridge jobs

What does this MR do?

Related to #233289 (closed)

We introduced inheriting variables from dependent jobs via dotenv report in %13.0. However, we did not consider bridge jobs to inherit variables, because bridge jobs do not download artifacts from dependencies.

With this MR, bridge jobs started to inherit variables of dependent jobs.

It is behind a feature flag ci_bridge_dependency_variables #273734 (closed).

❓ Question: Can it be a breaking change? Is there a possibility that an unintentionally inherited variable break the bridge job?

E2E test case issue: gitlab-org/quality/testcases#1086 (closed)

Screenshots (strongly suggested)

build:
  stage: build
  script: echo "MY_VAR=hello" >> variables.env
  artifacts:
    reports:
      dotenv: variables.env

trigger:
  stage: deploy
  variables:
    PASSED_MY_VAR: $MY_VAR
  trigger:
    include: .child.yml

downstream_test:
  stage: test
  script: echo $PASSED_MY_VAR

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team