feat(gravita): Support for Gravita app

[aliask]

Description

This PR adds support for displaying Gravita DeFi positions, including:

• Stability Pool deposits and rewards
• Vessel positions

Various tokens may be used as collateral for Vessels, all using the same contract address.
Each collateral type is represented as a separate position definition to support addresses with multiple Vessels.

⚠️ The Arbitrum network has not been tested, as visiting test URLs (e.g. http://localhost:5001/apps/gravita/positions?groupIds[]=vessel&network=arbitrum) displayed an empty response.
I've so far been unable to debug this issue, perhaps a dependency injection problem.

Checklist

• I have followed the Contributing Guidelines
• (optional) As a contributor, my Ethereum address/ENS is:
• (optional) As a contributor, my Twitter handle is:

How to test?

Note that the following addresses are picked randomly off the recent contract interactions, and may remove their positions.

Ethereum test addresses

• 0xc9442e6eecd5389d73322e965cd3fa488aaeee20 (rETH vessel and Stability pool deposit)
• 0x40f246f1cf7e20547a8ab503eb1dff59238a3dd0 (wstETH vessel)
• 0x361042cb65a69efde49bf68ceca58e4f44d6ced1 (wstETH vessel and Stability pool deposit)
• 0x8a83716acd66d9e1fb18c9b79540b72e04f80ac0 (swETH vessel)
• 0x00ee80c322d6e956d2629a73223605bbda946f2d (WETH vessel and Stability pool deposit)

Arbitrum test addresses (untested)

• 0xfe7b22071ab36a93a21df717bdc722b80e60c9d8 (rETH vessel)
• 0x12b3509f54a224277a71e36f86d936051506d025 (WETH vessel, Stability pool deposit)
• 0x97641A5f3EE3B0561c6BcC522F7E1BEdf2c2985a (wstETH vessel)

[wpoulin]

Thanks for your contribution, but there's already an existing Gravita app integration
Have a look at https://zapper.xyz/apps/ethereum/gravita?tab=assets
(It's in a private repo. but I'll update it and add support for Arbitrum)

[aliask]

I totally missed this. I had checked on Arbitrum and decided to add it when I saw it was missing from the app and the repo. 🤦
I wish it wasn't in a private repo so I didn't waste all this time re-implementing it!

Looking forward to the update though! 👍

[wpoulin]

I've updated the app integration and now balances are showing up properly on Arbitrum
https://zapper.xyz/apps/arbitrum/gravita?tab=assets

This PR isn't necessary anymore, but again, thanks for your contribution. Next time, make sure to have a look at the app page and if you don't see the app within Studio ping us on Discord