[DAR-3513][External] Addition of the item_merge_mode push argument

[JBWilkie]

Adds the item_merge_mode argument to push() :
item_merge_mode: Enum["slot", "series", "channel"]

1: It is available through both CLI & SDK-initiated push() with this syntax:
darwin dataset push /path/to/files --item_merge_mode [slots | series | channels]

from darwin.client import Client

team_slug = "team_slug"
dataset_slug = "dataset_slug"
files_to_upload = ["path/to/dir_1", "path/to/dir_2", "...", "path/to/dir_n"]
item_merge_mode = # oneof["slots" | "series" | "channels"]

client = Client.local()
dataset = client.get_remote_dataset(dataset_identifier=f"{team_slug}/{dataset_slug}")
dataset.push(files_to_upload=files_to_upload, item_merge_mode=item_merge_mode)

2: Raises an error if preserve_folders is set:
dataset.push(files_to_upload=files_to_upload, item_merge_mode=item_merge_mode, preserve_folders=True)

3: Throws 1 non-blocking warning for each instance of:

• A file path passed to push() that references a specific file rather than a directory, since these are ignored
• Each folder that after being parsed according to the specified item_merge_mode rules, results in an empty directory

Technical Implementation
1: Forks the existing parsing logic so that it's only run if item_merge_mode isn't set
2: If item_merge_mode is set, use parsing logic that creates 1 MultiFileItem object (new class) per dataset item. Run validation & construct + attach a Layout object to each MultiFileItem

Changes beyond this point would relate to uploading itself, so are beyond the scope of this ticket, and will be coming in the next couple of weeks

[linear]

DAR-3513 Add the `item_merge_mode` argument to `push()`

[wiz-inc-4ad3b29aa7]

Wiz Scan Summary

IaC Misconfigurations
Vulnerabilities
Sensitive Data
Total
Secrets

[JBWilkie]

Closing in favour of the multi-file-push branch PR: #923