Set a default value for exposure_timeout parameter in JUNGFRAUConditions

Description

The exposure_timeout parameter was added recently in !1066 (merged). It seems we have a logical default value of 25 which we ignore if specified, but we didn't put a default value in for JUNGFRAUCondition, so you have to pass it explicitly. When I synced this across to extra.calibration, a test which wasn't in this repo failed.

Is there a good reason to make it a required parameter? New required parameters mean breaking the API, whereas new optional ones don't.

How Has This Been Tested?

CI (added test in this MR)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Test (additional or refactored tests)

Checklist:

• My code follows the code style of this project.

Reviewers

@ahmedk @schmidtp