[CDF-25196, CDF-25195] 👽 Added default mappings from asset-centric to CogniteCore (#1760)

# Description

Stacked on #1761, #1767

**Context**: This is part of the `alpha` migration tooling in Toolkit,
for overview [see
here](https://cognitedata.atlassian.net/wiki/spaces/~170890702/pages/5455773697/Migration+Tooling+in+Toolkit).
This is part of step 1/prerequisite were we create default ViewSource
instances.

This PR adds the default mapping from asset/timeseries/files/event to
CogniteAsset/CogniteTimeSeries/CogniteFile/CogniteActivity. This will be
deployed to the migration model when the user run `cdf migrate prepare`.
Then, they will be used in the `cdf migrate
timeseries/events/assets/files` commands.


## Changelog

- [x] Patch
- [ ] Minor
- [ ] Skip

## cdf

### Added

- [alpha] The `cdf migrate prepare` now populates default view mappings.

## templates

No changes.


