Describe the bug
When you try to import proposals from a proposals component to another, the process is done in a server thread instead of in a background job. This might work fine for a small amount of proposals, but for Decidim Barcelona (importing >800 proposals) this means the process fails because the server/the infrastructure provider cancels the request.

This process should be moved to a background job.

To Reproduce

1. Create a proposals component with a huge amount of proposals (800 for example)
2. Create another proposals component in the same participatory space
3. Import proposals from the first component to the second one. Notice how it takes a lot of time, or the process fails, even.

Expected behavior
Not to receive an error. The process should be done in a background process.

Screenshots
None

Stacktrace
None

Extra data (please complete the following information):

• Decidim Version: 0.24.0.rc2

Additional context
None