Allow configuration of AWS Asset RemovalPolicy to prevent accidental deletion

[dmeehan1968]

I had added a Dynamo DB to my sst config, used it in the app including writing some data. In the process of my work I had to checkout a prior version which caused sst to destroy the DB, so I lost data (only a couple of records so just a minor inconvenience).

AWS CDK allows one to configure the removal policy for assets, to avoid the risk of inadvertant deletion. This does introduce some complications in terms of naming conflicts, and does potentially leave one needing to adopt an existing resource rather than creating a new one.

This may therefore be beyond the scope of SST and in the realms of backup/restore policies, even when in dev environments.