Rename --pruning and --keep-blocks to be more similar to one another (#11934)

* rename prunning and keep-blocks flags

* Add aliases in keep-blocks and pruning for backward compatibility

* Rename in code variables from  and  to  and

substrate/client/service/src/lib.rs

@@ -60,7 +60,7 @@ pub use self::{
 	error::Error,
 };
 pub use config::{
-	BasePath, Configuration, DatabaseSource, KeepBlocks, PruningMode, Role, RpcMethods, TaskType,
+	BasePath, BlocksPruning, Configuration, DatabaseSource, PruningMode, Role, RpcMethods, TaskType,
 };
 pub use sc_chain_spec::{
 	ChainSpec, ChainType, Extension as ChainSpecExtension, GenericChainSpec, NoExtension,