Introduce `Runtime` class to uniformly identify the running process

What does this MR do?

There are runtime switches scattered all over to execute/determine configuration based on which runtime environment we're in (puma/unicorn/sidekiq etc). This MR aims to consolidate this into a single access point.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Merge request performance guidelines
• Style guides

Availability and Testing

This was impossible to feature-flag since the code was so scattered across the code base, but the semantics shouldn't have changed, the checks just have moved behind an interface.

Closes #36709 (closed)