feat: download as CAR via the context menu

[hacdias]

Partially addresses #1798.

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License: MIT
Signed-off-by: Henrique Dias hacdias@gmail.com

[lidel]

@rvagg @olizilla @mikeal @alanshaw
Would appreciate some opinionated bikeshed around labels related to DAG export/import in UI (webui/desktop).

Does the above screenshot look sensible?

Mainly, I want this to be consistent with messaging we have in dev docs in other places (are we using "DAG export" or "CAR download" etc)?

[rvagg]

I think this is probably OK, we've put IPFS' "export" inside the "dag" subsection and it's technically correct that it's exporting an entire DAG starting from a root.

We have other place that are front-loading "CAR", like web3.storage which has a putCar() API (though not in docs yet I think), but I'm not sure that's the ideal approach as it would be good to have some wriggle room around transports for moving DAGs around and not box ourselves too tightly into a form. Even the putCar() API in web3.storage just means "give me an object that conforms to the CarReader API, which it then just uses as a simple root provider blockstore (I faked this for percid.va.gg so I could use that API but not deal with CARs).

[lidel]

LGTM but let's park this until we have a PR with import (#1838) as noted in #1798 (comment)

[hacdias]

@lidel I rebased and made the necessary updates to use the new gateway URLs and the nomenclature.

Notes:

1. I added some of the mechanics we use in feat: use direct links to download all files #1894 such that we don't store the whole file in memory downloading it. We create an artificial a block and click on it.
2. The gateway download doesn't follow the filename query parameter. I opened an issue in Gateway CAR Download Doesn't Respect filename kubo#9027 about it and made a PR: fix: honour url filename when downloading as CAR/BLOCK kubo#9028
3. I also don't understand why the CI is failing on "Installing Dependencies" as this PR changes nothing regarding dependencies.

Question:

1. Are we releasing this without feat: import DAG CAR #1838? feat: import DAG CAR #1838 requires updating Web UI with the new IPFS dependencies. We talked about introducing download only before (Import/export CAR DAG archives #1798 (comment)) but you were hesitant.

[lidel]

LGTM, this is unblocked because go-ipfs 0.13 supports ?format=car (release notes) and we now have PR with gateway specs at ipfs/specs#283

Needs small unicode fix below, but I'll apply it shortly.

Unsure why CI deps install fail, probably the usual NPM rot.
Will regenerate package-lock and see if that helps.