Strip leading & trailing whitespaces in CI/CD secret variable keys

What does this MR do?

1. This ensures that the key of a secret variable is stripped of leading and trailing whitespaces.
2. This EE MR ensure that the environment scope of a secret variable is stripped of leading and trailing whitespaces.

Why was this MR needed?

Because leading and trailing whitespaces should be stripped and can be confusing. See #40561 (closed).

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Related to #40561 (closed).