Add FUZZAPI_POSTMAN_COLLECTION_VARIABLES to API Fuzzing CI template

What does this MR do?

Pass a new variable FUZZAPI_POSTMAN_COLLECTION_VARIABLES to worker docker containers. This variable allows the user to set variable values for Postman Collections.

A changelog entry will be added to the documentation MR.

Relates to #273111 (closed)

CI Template

1. This change is backwards compatible.
2. No new spec tests have been added. This change passes an environment variable, doesn't change how the CI template logic works.
3. The API Fuzzing CI template doesn't yet have a latest version as the feature is less than 1 year old. All changes are being made to the stable version.

Test Project

The following test project makes use of the changes to the CI Template. The test is occurring on a branch "mike-test-template".

• Project
• CI Template
• Pipeline
• Pipeline Job

Screenshots (strongly suggested)

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

Related to #273111 (closed)