Export AWS Access Credentials If Needed

[ranchodeluxe]

Background

Workaround for #192 so that we don't have to change anything in titiler-pgstac

Changes

• adds VEDA_RASTER_EXPORT_ASSUME_ROLE_CREDS_AS_ENVS to APISettings
• adds VEDA_RASTER_EXPORT_ASSUME_ROLE_CREDS_AS_ENVS=True as defaults to UAH dev/staging env secrets
• adds a quick conditional check for VEDA_RASTER_EXPORT_ASSUME_ROLE_CREDS_AS_ENVS in get_gdal_config to know if it should export the assume-role creds. The reason this check exists is b/c we know Lambdas already inject AWS_* os env vars and this is a VERY hacky solution so we don't want to get used to these things being exported and also want to have a trail of why we did this for future us

Why It Works

• rasterio.Env uses thread local which means it inits a new empty context per thread

• So by the the time CustomSTACReader is retrieving the image in this line it's running inside of multiple threads. Each thread's CustomSTACReader triggers self.ctx (which is just rasterio.Env) and it has to start all over again with empty context when accessing the image.

• However, because we now export the AWS credentials into os env vars the nested rasterio.Env lookup will hit this check and re-init a new session: https://github.com/rasterio/rasterio/blob/main/rasterio/env.py#L204-L205