New API to download application packages

[eostis]

From #26104

Build an API to get all files from an active application to redeply it incrementally

(I noticed vespa-deploy fetch, but could not find the same fetch in the APIs)

Use case: an application package is already deployed with some schemas on a remote server or in the cloud. You want to add/remove/update a schema from it, without erasing other schemas. But you do not have access to the source of the last deployed files, nor to the server filesystem.

[johans1]

Add to application v4 and v2 and CLI, use it in the console

[bratseth]

Update: This is already in application/v4, so:

• Add "get package as zip" to application/v2
• Add command to CLI which uses application/v2 or v4 depending on target.

[eostis]

Closing inactive issue.

[bratseth]

On our backlog.

[baldersheim]

backlog or soon ....

[mpolden]

vespa fetch is available in 8.265.12.