Expand variables only when needed

What does this MR do?

This makes us to expand variables only when needed, instead of requesting all variables each time.

This specifically helps in situation when explicit name of environment: production is used.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Code review guidelines
• Merge request performance guidelines
• Style guides

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/47133

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/65538