Add hash command with base64 subcommand (#2769)

* WIP try testing hash command

Ensure test worked

fmt

WIP get it working for other types of base64

Use optional named arg

WIP

* rebased and refactored a little with encoding and decoding

Fix some typos

Add some more charactersets

refactor several args into the encoding config struct and fix character_set arg. It needs to match the field

Add main hash command so it can be found via help

Added tests for running the whole pipeline

* add test case to cover invalid character sets

* clippy and fmt

crates/nu-cli/tests/commands/mod.rs

@@ -20,6 +20,7 @@ mod flatten;
 mod format;
 mod get;
 mod group_by;
+mod hash_;
 mod headers;
 mod histogram;
 mod insert;