Extend returning info in the getValidators() API

[owl352]

Issue

To finish validators page (#152), we need to add few metadata fields in the response of the getValidators() query with such data:

Total proposed blocks count
Last proposed block height ( + timestamp)

Things Done

Now in response to getValidators and getValidatorByProTxHash query we get data of this format:

{
  "proTxHash": "F60A6BF9EC0794BB0CFD1E0F2217933F4B33EDE6FE810692BC275CA18148AEF0",
  "blocksCount": 5,
  "lastProposedBlockHeader": {
    "height": 5,
    "timestamp": "2024-06-23T13:51:44.154Z",
    "hash": "7253F441FF6AEAC847F9E03672B9386E35FC8CBCFC4A7CC67557FCA10E342904",
    "l1LockedHeight": 1337,
    "appVersion": 1,
    "blockVersion": 13
  }
}

To get the new fields it was necessary to realize one more database access, but already in the blocks table, then process the data and after that produce a response.
Tests have also been adjusted to work with the new data
README.md was updated with information about getValidators and getValidatorByProTxHash

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Name	Status	Preview	Comments	Updated (UTC)
platform-explorer-zham	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 26, 2024 1:35pm

[pshenmic]

Thank you! Looks good to me