Add export button to Data Explorer

[dwrth]

Description

This PR adds an export button to the Data Explorer and adjusts the helper functions in transformToCsv.ts and transformToJson.ts.

Validation

Edit: new location of the export button

Related Issues

Resolves #1409

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0
  license.
• I have run pnpm checks to ensure code compiles and meets standards.
• I have run pnpm test to check if all tests are passing.
• I have covered new added functionality with unit tests if necessary.
• I have added an entry in the Changelog.md.

[kmcginnes]

This is great @dwrth. I'm focused on other tasks, so I can't jump on this just yet.

I think this is a small enough feature I can dedicate soon to review and test.

[kmcginnes]

In regards to this comment:

For now the option "Keep filtering and sorting" obviously has no use but it will have, once is #1408 is implemented.

I don't think "Keep filtering and sorting" will ever make sense in this context. Since Data Explorer needs to work on server side paging/filtering/sorting then unchecking "Keep filtering and sorting" would imply that all nodes for the selected node type would be exported. I just don't think that is a realistic goal for any database of a reasonably large size (most users of Graph Explorer).

So I think we will always want to export whatever is in the current view, which would essentially mean "Keep filtering and sorting" is always checked.

[kmcginnes]

Oh, and take a look at this PR:

• Tweak navigation button UI & data explorer toolbar #1459

It is essentially removing that second nav bar in data explorer. So your new button will need to be moved to the PanelHeader somewhere.

[dwrth]

@kmcginnes I merged the changes and moved the button to a new location. Also adjusted the export modal to hide the filter checkbox and force the 'only current page' checkbox

[kmcginnes]

I tested this locally, and it looks pretty good. The main issue is hiding the "Only current page" option.

This will make the options list empty, so we should also hide the whole "Options" section.

The rest of my comments are cleanup and tests.