Bulk copy from proposal

Description:
The idea is to allow users to copy all or selected parts of data from another proposal. In many cases, copying the entire proposal and then removing unnecessary parts might be sufficient. However, there may be use cases where users need to combine large sets of data from multiple proposals.

Now that we have the bulk edit feature working for the entities that tend to grow the most (e.g., tasks, resources, and resource estimates), we can take this a step further by allowing users to select a different proposal as the input source for bulk editing. Additionally, since the bulk edit feature will continue to evolve, the new "bulk copy from proposal" capability can grow alongside it, benefiting from future enhancements.

Use Case / Example:
If a user previously split a large proposal into several smaller ones due to performance issues—which have now been resolved—they may want to merge the data back into a single proposal.