container/ps: add HealthStatus formatter field

[Mohammed-Thaha]

- What I did

Added a new docker ps --format placeholder: .HealthStatus, so users can print container health state directly as a dedicated field.

• Fixes update docs, tests, local changes for "HealthCheck" in "ps" response #6203
• relates to Add HealthStatus attribute on the docker ps command moby/moby#50281

- How I did it

• Added HealthStatus() to the container formatter context.
• Returned health directly from c.c.Health.Status when available.
• Added fallback parsing from .Status text for:
  • (healthy) -> healthy
  • (unhealthy) -> unhealthy
  • (health: starting) -> starting
• Updated docs in docs/reference/commandline/container_ls.md to include .HealthStatus in the format placeholders table.
• Added/updated unit tests in cli/command/formatter/container_test.go.

- How to verify it

1. Start dev shell:

   make -f docker.Makefile shell

2. Build the CLI binary:

   make binary

3. Run a container that stays in starting during the start period:

   docker rm -f hc-starting 2>/dev/null || true
   
   ./build/docker-linux-amd64 run -d --name hc-starting \
     --health-cmd='exit 1' \
     --health-start-period=2m \
     --health-interval=5s \
     --health-retries=1 \
     alpine sh -c 'sleep 300'

4. Verify formatter output:

   ./build/docker-linux-amd64 ps -a --filter name=hc-starting --format "table {{.Names}}\t{{.Status}}\t{{.HealthStatus}}"

Expected result:

• STATUS contains (health: starting)
• HEALTHSTATUS shows starting

- Human readable description for the release notes

`docker ps --format` now supports a `.HealthStatus` placeholder to print container health state (`starting`, `healthy`, `unhealthy`) as a dedicated field.

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Thanks for working on this! I left some comments/suggestions; feedback welcome!

[thaJeztah]

I think we should name this HealthStatus, as it's not showing information about the health-check otherwise.

[thaJeztah]

It'd be good to reference the API version that introduced the new field to save future visitors of this code to decide whether the fallback is still needed (and perhaps a link to the pull request for future reference);

// Fallback for API versions before v1.52,  which include health only in Status text;
// see https://github.com/moby/moby/pull/50281
// see https://github.com/moby/moby/blob/docker-v29.4.3/daemon/container/health.go#L18-L43

[thaJeztah]

Perhaps we should slightly optimise here; also adding an early return; something like;

_, health, ok := strings.Cut(c.c.Status, "(")
if !ok || !strings.HasSuffix(health, ")") {
	return ""
}


health = strings.TrimSuffix(health, ")")
health = strings.TrimPrefix(health, "health: ")

switch container.Health(health){
case container.Healthy, container.Unhealthy, container.Starting:
	return health
default:
	return ""
}

Slightly ugly because of the health: prefix but it makes it slightly more explicit that we're matching specific states.

[Mohammed-Thaha]

Used parsedHealth := container.HealthStatus(health) before the switch so the parsed value matches the container.Healthy, container.Unhealthy, and container.Starting typed constants during comparison.

[thaJeztah]

Related to my other comment; perhaps HEALTH STATUS