add options attribute to inputs_for/1

[woylie]

Phoenix.HTML.FormData.to_form/4 allows for arbitrary protocol-specific options to be passed in the fourth argument. Phoenix.Component.inputs_for/1 currently only supports options specific to the protocol implementation for Ecto.Changeset. This PR adds a new options attribute that can be used to pass any additional options for other implementations.

Context: Flop.Phoenix implements the FormData protocol for the Flop.Meta struct and relies on a fields option to be passed. This is currently only possible with the inputs_for/4 function that was moved to PhoenixHTMLHelpers, but not with the inputs_for component.

Relates to woylie/flop_phoenix#299.

[josevalim]

For completeness, can you give an example of the options you would pass here?

[woylie]

For completeness, can you give an example of the options you would pass here?

In the case of Flop.Phoenix, you can pass additional options like the filter operators: fields: [{:email, op: :ilike}]. The FormData implementation adds the operator to form.hidden.

[josevalim]

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