Clowder: parameterize ENABLE_SIGNING and GNUPGHOME

[drodowic]

No-issue

Description 🛠

parameterize ENABLE_SIGNING and GNUPGHOME envvars in the clowder config to allow ephemeral to be deployed differently from stage and prod

Reviewer Checklists 👀

Developer reviewer:

• Code looks sound, good architectural decisions, no code smells
• There is a Jira issue associated (note that "No-Issue" should be rarely used)
• Tests are included in galaxy_ng/tests/integration or galaxy_ng/tests/functional, and they fully cover necessary test scenarios… or tests not needed

QE reviewer (exceptions):

• Tests are included in galaxy_ng/tests/integration or galaxy_ng/tests/functional, and they fully cover necessary test scenarios… or tests not needed
• PR meets applicable Acceptance Criteria for associated Jira issue

Note: when merging, include the Jira issue link in the squashed commit