Allow users to export/import p2p keys

[spylogsster]

Placeholder for import/export p2p keys

ipfs key export -o ./mykey.key mykey
ipfs key import anotherkey ./mykey.key

add "..." instead of a trash icon for keys and there's a submenu for remove and export keys

[MrCrypticxDev]

Yeah that seems reasonable.

[spylogsster]

the export part will be done after ipfs/kubo#8113

[stephendonner]

Verified PASSED using the testplan from brave/brave-core#8777 with build

Brave	1.26.43 Chromium: 91.0.4472.77 (Official Build) beta (x86_64)
Revision	1cecd5c8a856bc2a5adda436e7b84d8d21b339b6-refs/branch-heads/4472@{#1246}
OS	macOS Version 11.4 (Build 20F71)

Check if IPFS import works as expected and files/directories/links are imported well

Steps:

1. new profile, launch Brave
2. load ipns://brantly.eth
3. click on Use a local node
4. load https://www.wikipedia.org/
5. context-click on the page and choose Import to IPFS > This page
6. wait
7. paste the link from the clipboard; ensured https://dweb.link/ipfs/QmXw6iHkf19YiEpydfUFbK4QegyRzyf1yCVaSEHsLUyMiW?filename=www.wikipedia.org loaded

Confirmed the imported and shared resource loads correctly; more verifications for import were already done over in https://github.com/brave/brave-browser/issues/16020.

Export keys from node on any computer via ipfs key export -o ./mykey.key mykey command and import it via brave://settings/ipfs/keys

(To save time, I used an exported key given to me by @spylogsster 👍 )

(Import) Steps:

1. new profile, launch Brave
2. loaded ipns://brantly.eth
3. click on Use a local node
4. loaded brave://settings/ipfs
5. clicked on Set up your IPNS keys
6. clicked Add
7. typed mynewgoodkey and clicked Import
8. browsed to mykey.key and clicked Import
9. loaded https://ia801003.us.archive.org/26/items/1941themaltesefalconelhalconmaltesjohnhuston/1941%20-%20The%20Maltese%20Falcon%20-%20El%20halc%C3%B3n%20malt%C3%A9s%20-%20John%20Huston%20-%20VOSE.ogv
10. context-clicked page and chose Save video as..., clicked Save
11. clicked the "hamburger" menu and chose Share Local File Using IPFS
12. chose mynewgoodkey from the flyout menu
13. chose previously-saved Maltese-Falcon video, chose Open
14. waited
15. pasted the copied-to-clipboard link and loaded The Maltest Falcon
16. compared the file hash to the published-key's hash

Confirmed that they match (...ijwujypbywjd1).

(Generate/export) Steps:

1. new profile, launch Brave
2. loaded ipns://brantly.eth
3. click on Use a local node
4. loaded brave://settings/ipfs
5. clicked on Set up your IPNS keys
6. clicked Add
7. typed myexportedkey and clicked Generate
8. browsed to mykey.key and clicked Open
9. loaded https://ia801003.us.archive.org/26/items/1941themaltesefalconelhalconmaltesjohnhuston/1941%20-%20The%20Maltese%20Falcon%20-%20El%20halc%C3%B3n%20malt%C3%A9s%20-%20John%20Huston%20-%20VOSE.ogv
10. context-clicked page and chose Save video as..., clicked Save
11. clicked the "hamburger" menu and chose Share Local File Using IPFS
12. chose myexportedkey from the flyout menu
13. chose previously-saved Maltese-Falcon video, chose Open
14. waited
15. pasted the copied-to-clipboard link and loaded The Maltest Falcon
16. compared the file hash to the published-key's hash

Confirmed they match (...4nhaje1yu1r).

Check if you try to import anything other than a key file, we alert an error on import attempts

Steps:

1. new profile, launch Brave
2. load ipns://brantly.eth
3. click on Use a local node
4. downloaded a 10 mb file: http://mirror.sfo12.us.leaseweb.net/speedtest/10mb.bin
5. loaded brave://settings/ipfs
6. clicked on Set up your IPNS keys
7. clicked Add
8. typed mynewboguskey and clicked Import

Confirmed I got an error message in red: 'mynewboguskey' key import failed beneath Keys available for publishing.