Enforce required, optional, and rest positional arguments start with an uppercase and end with a period. (#11285)

# Description

This updates all the positional arguments (except with
`--features=dataframe` or `--features=extra`) to start with an uppercase
letter and end with a period.

Part of #5066, specifically [this
comment](/nushell/nushell/issues/5066#issuecomment-1421528910)

Some arguments had example data removed from them because it also
appears in the examples.

There are other inconsistencies in positional arguments I noticed while
making the tests pass which I will bring up in #5066.

# User-Facing Changes

Positional arguments are now consistent

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

Automatic documentation updates

crates/nu-command/src/system/run_external.rs

@@ -47,8 +47,8 @@ impl Command for External {
                 None,
             )
             .switch("trim-end-newline", "trimming end newlines", None)
-            .required("command", SyntaxShape::String, "external command to run")
-            .rest("args", SyntaxShape::Any, "arguments for external command")
+            .required("command", SyntaxShape::String, "External command to run.")
+            .rest("args", SyntaxShape::Any, "Arguments for external command.")
             .category(Category::System)
     }