Unify the manifest.json

[pankajastro]

Currently, we have checked in manifest.json at multiple places example

https://github.com/astronomer/astronomer-cosmos/blob/main/tests/sample/manifest_source.json
https://github.com/astronomer/astronomer-cosmos/blob/main/dev/dags/dbt/jaffle_shop/target/manifest.json

As a result, many times, both files diverge and result in unexpected results during the test.

For example, we have test https://github.com/astronomer/astronomer-cosmos/blob/0edb07d6b58827ebf66fbc82a062ea0a5cfb0717/tests/dbt/test_graph.py#L614 which run for dbt ls and manifest and in both cases it uses different manifest file and it results in unexpected failure because manifest_source.json is not latest.