Add support for built-in retry policies

[adespawn]

Those are:

• Default Retry Policy
• FallthroughRetryPolicy

The full support requires following elements:

• Working code
• Documentation of how the policies work
• Migration guide (The default behaviour is changing)
• Enabling tests

[adespawn]

Regarding documentation about retry policies, I would prefer to have a copy of what is documented in the Rust driver, rather than attempting to create something on my own. But the documentation in the Rust driver is a bit lacking (scylladb/scylla-rust-driver#1285).

For this reason, I will write only partial documentation, and come back to this once the aforementioned issue is resolved.

[adespawn]

Considering that the retry policies are added, and the only missing part are integration tests (that require a bit more work: - adding support for address translation and ability to control rust-proxy) I'm moving the remaining part of this issue to GA