[Epic] Snapshots as a First Class Citizen

[gshank]

An epic to improve the usability and accuracy of snapshots.

### P0 - must
- [ ] https://github.com/dbt-labs/dbt-core/issues/4000
- [ ] https://github.com/dbt-labs/dbt-core/issues/10326
- [ ] https://github.com/dbt-labs/dbt-core/issues/10325
- [ ] https://github.com/dbt-labs/dbt-core/issues/10301
- [ ] https://github.com/dbt-labs/dbt-core/issues/10234
- [ ] https://github.com/dbt-labs/dbt-core/issues/10185
- [ ] https://github.com/dbt-labs/dbt-core/issues/10246
- [ ] https://github.com/dbt-labs/dbt-core/issues/10187
- [ ] https://github.com/dbt-labs/dbt-core/issues/10235
- [ ] https://github.com/dbt-labs/dbt-core/issues/10921

### P1 - should
- [ ] https://github.com/dbt-labs/dbt-core/issues/9992
- [ ] https://github.com/dbt-labs/dbt-core/issues/10372
- [ ] https://github.com/dbt-labs/dbt-core/issues/10236
- [ ] https://github.com/dbt-labs/dbt-core/issues/7867
- [ ] https://github.com/dbt-labs/dbt-core/issues/8207
- [ ] https://github.com/dbt-labs/dbt-core/issues/7869
- [ ] https://github.com/dbt-labs/dbt-core/issues/10300

### p2 - could
- [ ] https://github.com/dbt-labs/dbt-core/issues/10438
- [ ] https://github.com/dbt-labs/dbt-core/issues/7138
- [ ] https://github.com/dbt-labs/dbt-core/issues/10320

### revisit, refine, prioritize
- [ ] https://github.com/dbt-labs/dbt-core/issues/3878
- [ ] https://github.com/dbt-labs/dbt-core/issues/4661
- [ ] https://github.com/dbt-labs/dbt-core/issues/2848
- [ ] https://github.com/dbt-labs/dbt-adapters/issues/82
- [ ] https://github.com/dbt-labs/dbt-core/issues/8885

### Base adapter
- [ ] https://github.com/dbt-labs/dbt-adapters/pull/317
- [ ] https://github.com/dbt-labs/dbt-adapters/pull/321
- [ ] https://github.com/dbt-labs/dbt-adapters/pull/290
- [ ] https://github.com/dbt-labs/dbt-adapters/pull/326

### Concrete adapters
- [ ] https://github.com/dbt-labs/dbt-postgres/pull/180
- [ ] https://github.com/dbt-labs/dbt-redshift/pull/964
- [ ] https://github.com/dbt-labs/dbt-snowflake/pull/1271
- [ ] https://github.com/dbt-labs/dbt-bigquery/pull/1428
- [ ] https://github.com/dbt-labs/dbt-spark/pull/1154
- [ ] https://github.com/dbt-labs/dbt-postgres/pull/152
- [ ] https://github.com/dbt-labs/dbt-spark/pull/1113
- [ ] https://github.com/dbt-labs/dbt-postgres/pull/145
- [ ] https://github.com/dbt-labs/dbt-spark/pull/1097

Discussions

Problems & (Potential) Solutions for Snapshots
Toggling values when snapshotting a table with a key violation

[danielefrigo]

another interesting customization could be the ability to configure the value for dbt_valid_to then opening a new record.
dbt default is null, but in many cases I found the need to have a far away timestamp (e.g. '2999-12-31').

[graciegoheen]

@danielefrigo Yes! This is something we'd like to do - issue here -> #10187

[jeremyyeo]

Snapshots currently don't support contracts. Would be great have snapshots support contracts/constraints just as models do.

[graciegoheen]

Thanks @jeremyyeo - would you be down to open up a new issue for that feature request?

[graciegoheen]

Closing this EPIC out since we've closed the issues slated for the 1.9 release - will open up a new EPIC if we pick up more of these in the future