Support groupings in BindPFlags

[heaths]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

When you define pflags like so:

rootCmd.PersistentFlags().StringVar(&opts.Color.Comment, "color-comment", defaultColorComment, fmt.Sprintf("Hex RGB color code for comments e.g., %q.", defaultColorComment))
rootCmd.PersistentFlags().StringVar(&opts.Color.Error, "color-error", defaultColorError, fmt.Sprintf("Hex RGB color code for errors e.g., %q.", defaultColorError))
v.BindPFlags(rootCmd.PersistentFlags())

The flag name e.g., "color-comment" is not automatically matched to a section like so:

color:
  comment: "#00ff00"

Proposed Solution

When calling BindPFlags, any long name that is separated by certain characters e.g., "-" or ".", would automatically consider any prefixes to be a section e.g.,

"foo-bar-baz" would look for:

foo:
  bar:
    baz: ""

To avoid backcompat issues, this could be an Option set either in NewWithOptions or via explicit function call.

Alternatives Considered

No response

Additional Information

There is a workaround after reading #375 (comment), but it requires binding individual flags.

[github-actions]

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