The local strategies, in order, to use for the given mnemonic - the first applicable strategy is used. For example, `worker,sandboxed` runs actions that support persistent workers using the worker strategy, and all others using the sandboxed strategy. If no mnemonic is given, the list of strategies is used as the fallback for all mnemonics. The default fallback list is `worker,sandboxed`, or`worker,sandboxed,standalone` if `experimental_local_lockfree_output` is set. Takes [mnemonic=]local_strategy [,local_strategy,...]