Add contracts endpoint

[moisses89]

Description

• Add the contracts endpoint following the next schema

{
  "count": 0,
  "next": "string",
  "previous": "string",
  "results": [
    {
      "address": "string",
      "name": "string",
      "display_name": "string",
      "chain_id": 0,
      "project": {
        "description": "string",
        "logo_file": "string"
      },
      "abi": {
        "abi_json": [
          {}
        ],
        "abi_hash": "string"
      }
    }
  ]
}

• Implement pagination for this endpoint and for future endpoints

Issue related

Close #12

[coveralls]

Pull Request Test Coverage Report for Build 12430455829

Details

• 116 of 124 (93.55%) changed or added relevant lines in 8 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.9%) to 89.268%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
app/routers/contracts.py	11	13	84.62%
app/routers/models.py	33	35	94.29%
app/services/contract.py	6	8	75.0%
app/services/pagination.py	38	40	95.0%

Files with Coverage Reduction	New Missed Lines	%
app/services/contract.py	1	78.57%

Totals
Change from base Build 12375882360:	0.9%
Covered Lines:	366
Relevant Lines:	410

---

💛 - Coveralls

[Uxio0]

Passing the request to the service and instantiating one service for every client does not sound right to me