Add Literal type hint for `DBSnapshotTypeDef["SnapshotType"]`, and others

[DeflateAwning]

Describe your idea
Currently SnapshotType, as related to RDS backups, used in a variety of places, is annotated as SnapshotType: NotRequired[str]. It would be better if it was annotated as follows:

SnapshotType_t = Literal[
    "automated",  # Daily backups from last week in RDS.
    "manual",  # Manual snapshots created by users, e.g., right before deleting a database.
    "shared",
    "public",
    "awsbackup",  # Weekly backups from AWS Backup.
]

The list of valid values is here: https://docs.aws.amazon.com/AmazonRDS/latest/APIReference/API_DescribeDBSnapshots.html

[vemel]

Hello. Thank you for the report.

I build literal using botocore shapes, so SnapshotType must be str instead of enum there. I can add a hardcoded enum in place of ShapshotType, but output type from methods would still be str. I will investigate if is safe to do it.