Support post conditions that accept a range of stage statuses

For users of declarative pipeline, there are problems with coding 'post' conditions to handle stages that might come up as UNSTABLE rather than SUCCESS if a test fails. This means if a stage is unstable, then the 'success' condition will break. See example: https://issues.jenkins.io/browse/JENKINS-39203?focusedCommentId=350537&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-350537

Solving this requires writing separate post conditions for each possible status.

Instead, it would be very good to support a 'statusGreaterThanOrEqual' condition that takes a Result code and runs if it's better than it (and perhaps statusLessThan, etc).