Fix executeUpgradeHandler ID parsing and error response

[thomaspanf]

Resolves the following issue:

tpan@tpan-meerkat:~$ rp4 o u eu
Please select a proposal to execute:
1: All available proposals
2: proposal 2 (name: 'rocketDAOProtocolVerifier', type: 'UpgradeContract', upgrade address: '0xc4D85aA3e318c38005F6D73cC53E5A2b4223723a', upgrade ABI: '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')
2

+============== Suggested Gas Prices ===============+
|   Speed   |    Max Fee   |      Total Gas Cost     |
| Fast      | 1.05662 gwei | 0.000000 to 0.000000 ETH |
| Standard  | 1.05147 gwei | 0.000000 to 0.000000 ETH |
| Slow      | 1.05135 gwei | 0.000000 to 0.000000 ETH |
+====================================================+

These prices include a maximum priority fee of 1.0000 gwei.
Please enter your max fee (including the priority fee) or leave blank for the default of 1.05662 gwei:


Using a max fee of 1.057 gwei and a priority fee of 1.000 gwei.
Are you sure you want to execute 1 proposals? [y/n]
y

Could not execute proposal 2: Could not execute upgrade proposal: invalid API response.

• We need .FormValue("id") instead of .URL.Query().Get("id") to properly parse the ID.
• WriteErrorResponse() returns the actual error instead of a generic invalid API response

Verification:

Before:

$ curl -s -X POST http://123.4.5.6:7890/api/upgrade/execute-upgrade \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -H "Authorization: Bearer <api-token>" \
  -d "id=999"
{"status":"error","error":"invalid API response"}

After:

$ curl -s -X POST http://123.4.5.6:7890/api/upgrade/execute-upgrade \
  -H "Content-Type: application/x-www-form-urlencoded" \
  -H "Authorization: Bearer <api-token>" \
  -d "id=999"
{"status":"error","error":"error executing trusted node DAO upgrade 999: error estimating gas needed: execution reverted: Invalid trusted node","txHash":"0x0000000000000000000000000000000000000000000000000000000000000000"}

[github-actions]

Coverage Report

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/rocket-pool/smartnode/rocketpool/api/upgrade	0.20% (ø)

---

Coverage by file

Changed files (no unit tests)

Changed File	Coverage Δ	Total	Covered	Missed	🤖
github.com/rocket-pool/smartnode/rocketpool/api/upgrade/execute-upgrade.go	0.00% (ø)	2322	0	2322

Please note that the "Total", "Covered", and "Missed" counts above refer to code statements instead of lines of code. The value in brackets refers to the test coverage of that file in the old version of the code.