Fix BED-8727: Add a default schema contract for DLT collection pipeline

[d3vzer0]

This change sets the following (default) DLT schema contracts:

entity	new	old	description
new tables	evolve	evolve	Not changed, already default DLT behaviour
new columns	evolve	evolve	Not changed, already default DLT behaviour
data type changes	discard_row	freeze	Instead of failing the pipeline, skip/discard the resource

This prevents the pipeline from failing when the data type of a single column does not match our expected schema. This change will discard the row and continue processing the pipeline by default. This can still be modified by supplying the --data-type-contract=freeze CLI option when strict data checks are needed:

╭─ Options ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│ --progress                  [tqdm|log|alive_progress]    Select progress tracker option [default: tqdm]                                                                                                                                                                                                                                                                         │
│ --tables-contract           [evolve|freeze|discard_row]  DLT contract applied when data contains newly seen resources/tables previously not collected [default: evolve]                                                                                                                                                                                                         │
│ --columns-contract          [evolve|freeze|discard_row]  DLT contract applied when data contains values/keys not found in the Pydantic model [default: evolve]                                                                                                                                                                                                                  │
│ --data-type-contract        [evolve|freeze|discard_row]  DLT contract applied when fields do not match the data types defined in the Pydantic model [default: discard_row]       

[d3vzer0]

discard_value is a supported contract but not supported when using Pydantic models, which is what we use for all the collectors