Export explorations

[Anish9901]

Fixes #4619

Adds the ability to export saved explorations along with applied transformations as a CSV file.

The "Export" button on the data explorer page has the following hover text and state:

• When there are no columns in an unsaved exploration(button disabled and no help text):

  

• When the exploration is unsaved(button disabled with help text):

  

• When the exploration is saved(button enabled with help text):

  

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

Developer Certificate of Origin

Developer Certificate of Origin

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
1 Letterman Drive
Suite D4700
San Francisco, CA, 94129

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.

[mathemancer]

Backend code mostly looks good, but I did have a suggestion to tidy up the chunking logic.

Given that this way of doing things requires holding the entire result in memory, please add a hard limit somewhere to keep the service safe. This should probably be in the chunker or something. No more than (say) 50k rows should ever be fetched and returned.

[mathemancer]

Backend code looks good, if you merge my suggestion. Otherwise, re-request review, please!

Please wait for another frontend review after sorting out the UI behavior when the limit cap is reached (e.g., throwing a warning, some tooltip, whatever)

[pavish]

@Anish9901 I had one comment.

As discussed in the engineering call, I'll take a look again once the tooltip to inform the user that the export would be limited to 50k rows is implemented.

[Anish9901]

@pavish I've added the changes for:

• 50k limit within the tooltip
• Using a Button instead of AnchorButton while disabling the "Export" button.

in this commit --> 4eb9a9b

[pavish]

@Anish9901 The code changes look good. Nice work!

I added a small commit to make the text displayed to the user a bit more friendly: 39ebcb7