Overwrite incremental strategies

[rainermensing]

resolves CT-1880

Description

Adding valid_incremental_strategies to redshift, thus overwriting inheritance from core. This is necessary in order to enable "merge" strategy for postgres 15

    def valid_incremental_strategies(self):
        """The set of standard builtin strategies which this adapter supports out-of-the-box.
        Not used to validate custom strategies defined by end users.
        """
        return ["append", "delete+insert"]

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR (included in original feature request)
• I have run changie new to create a changelog entry

[Kamalakar4Pelago]

Appreciate, the great work and discussion on this change,
May we know, any expected date on this, We would be happy to adapt and test ASAP.

[joydeepml]

Wondering if this is required as Redshift also supports "merge" as per the following doc?
https://docs.aws.amazon.com/redshift/latest/dg/r_MERGE.html

[dataders]

thanks @rainermensing for making this work so easy for us here! I'm closing this because this change was introduced via #251 (direct link to addition) at almost the same time as you.

no action item here for you, but what's next to bring merge to dbt-redshift is:

1. we (dbt Labs) merges Add merge incremental strategy for postgres dbt-core#6951,
2. @jiezhen-chen closes [ADAP-437] [Feature] Enable "merge" incremental strategy for Redshift #402 by mirroring the above PR but for dbt-redshift