Add "is the donation anonymous" to GIVbacks API export

[laurenluz]

I want an extra column in the data that Ashley grabs from the givbacks API each round that shows whether the donor selected the "donate anonymously" button, or not.

cc @WhyldWanderer

[mohammadranjbarz]

@WhyldWanderer @maryjaf It's on staging and is ready for the test

[maryjaf]

I made an anonymous donation and I see the below response in givback api,
this field is added in response :
"anonymous": true,
[
{
"amount": 5,
"currency": "GIV",
"createdAt": "2024-09-26-06:25:10",
"valueUsd": 5,
"anonymous": true,
"bottomRankInRound": 35,
"givbacksRound": 51089,
"projectRank": 22,
"givbackFactor": 0.61470586,
"valueUsdAfterGivbackFactor": 3.0735293,
"giverAddress": "0xa1179f64638adb613ddaac32d918eb6beb824104",
"txHash": "0x8a10dc5e0846d1380f5bb43a2ea6a54ac51f6b98931095687d7178907096578b",
"network": "optimism-sepolia",
"source": "giveth.io",
"giverName": "mary jafarimehr",
"giverEmail": null,
"projectLink": "https://giveth.io/project/mejan",
"isReferrerGivbackEligible": false,
"referrerWallet": null
},

---

if the donation isn't an anonymous donation, this field is set false as expected in response
"anonymous": false