Add support for downloading published Artifactory build-info object from Artifactory and append using the Jenkins-jfrog-plugin

### Is your feature request related to a problem? Please describe.

Consider the following use case where we are running a multi-branch pipeline that is having 3 new branches within it(i.e branch1, branch2, and master maintaining the same build name & number) and maintain a single buildinfo object in Artifactory by publishing it from each branch.
1. Publish buildinfo of the first pipeline branch to Artifactory
2. Then, download the existing buildinfo of the above build from Artifactory and append it to the current buildinfo of the next branch, and publish it again to Artifactory.
3. Similarly, download the latest buildinfo (for the above build number) from Artifactory and append it to the current buildinfo, and publish it to Artifactory.

### Describe the solution you'd like to see

Currently, appending a published build-info into an unpublished build-info is not supported. Hence, Looking for an option to download buildinfo object which was published as part of the previous build stage, and append it to the current stage build object so that we can maintain an aggregated buildinfo of the multi-branch pipeline.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Start by reviewing the Jenkins JFrog plugin's existing build-info publishing and append behavior, then inspect how Artifactory build-info objects are represented and transferred. Done means a published build-info can be downloaded, appended to the current build-info, and republished for successive pipeline branches; add coverage for the multi-branch aggregation flow.

Written by the indexing model from the issue text.