Change html representation to reflect laziness of catalog

[delucchi-cmu]

Feature request

In the _repr_html method, let's figure out how to make clear that the catalog's data has not been loaded. This may be in removing the dataframe, or indicating that this is a dummy dataframe only.

e.g. in https://github.com/astronomy-commons/lsdb/blob/main/src/lsdb/catalog/dataset/dataset.py#L32

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Please check the following:

• I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
• I have included any relevant links, screenshots, environment information, and data relevant to implementing the requested feature, as well as pseudocode for how I want to access the new functionality.
• If I have ideas for how the new feature could be implemented, I have provided explanations and/or pseudocode and/or task lists for the steps.

[nevencaplar]

Superseded by #399