bugfix: Prevent default TCP checks from being re-added on reload/restart

[anilvpatel]

Description

This PR fixes an issue where default TCP checks were being re-added on service reload or agent restart, even when they were explicitly disabled or replaced with custom checks during the initial service registration.

With this change, the agent now consistently preserves the original sidecar check configuration, ensuring default checks are added only when intended.

Testing & Reproduction steps

1. Start the consul agent
   consul agent -dev -data-dir=/tmp/consul/data

2. Register below hello service definition
   consul services register hello-service.json

{
  "service": {
    "id": "service-hello-1",
    "name": "service-hello",
    "port": 5050,
    "address": "127.0.0.1",
    "connect": {
      "sidecar_service": {
        "checks": [{
          "alias_service": "web",
          "name": "Connect Sidecar Aliasing web"
        }],
        "proxy": {
          "upstreams": [
            {
              "destination_name": "service-response",
              "local_bind_port": 9090
            }
          ]
        }
      }
    },
    "check": {
      "http": "http://127.0.0.1:5050/health",
      "interval": "10s"
    }
  }
}

3. As as sidecar service contains the checks, it does not added the default TCP checks
   http://127.0.0.1:8500/v1/health/service/service-hello-sidecar-proxy?dc=dc1

4. consul reload or restart the agent
   consul reload

5. After reload, its inconsistence and defaults TCP checks are added
   http://127.0.0.1:8500/v1/health/service/service-hello-sidecar-proxy?dc=dc1

PR Checklist

• [x ] updated test coverage
• external facing docs updated
• [ x] appropriate backport labels added
• [x ] not a security concern

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.

• If applicable, I've documented the impact of any changes to security controls.

  Examples of changes to security controls include using new access control methods, adding or removing logging pipelines, etc.

[hc-github-team-consul-core]

📣 Hi @anilvpatel! a backport is missing for this PR [23088] for versions [1.18,1.20,1.21] please perform the backport manually and add the following snippet to your backport PR description:

<details>
	<summary> Overview of commits </summary>
		- <<backport commit 1>>
		- <<backport commit 2>>
		...
</details>

[hc-github-team-consul-core]

📣 Hi @anilvpatel! a backport is missing for this PR [23088] for versions [1.18,1.20,1.21] please perform the backport manually and add the following snippet to your backport PR description:

<details>
	<summary> Overview of commits </summary>
		- <<backport commit 1>>
		- <<backport commit 2>>
		...
</details>

[hc-github-team-consul-core]

📣 Hi @anilvpatel! a backport is missing for this PR [23088] for versions [1.18,1.20,1.21] please perform the backport manually and add the following snippet to your backport PR description:

<details>
	<summary> Overview of commits </summary>
		- <<backport commit 1>>
		- <<backport commit 2>>
		...
</details>