Merge properties now available in on-merge checks invocation payload

[#1]

Hi all,

As requested on https://jira.atlassian.com/browse/BCLOUD-23049 we have added a mergeProperties field to the invocation payload of bitbucket:mergeCheck Forge function triggered by on-merge trigger, it contains merge commit message amongst other properties related to a pull request merge. 

For details see https://developer.atlassian.com/platform/forge/changelog/#CHANGE-1898.

Thanks

Wendy