[Docker]: Change Docker socket for Docker provider in Fleet managed agent

### Integration Name

Docker [docker]

### Dataset Name

container_logs

### Integration Version

2.14.0

### Agent Version

9.1.3

### OS Version and Architecture

Debian 12

### User Goal

Change the Docker socket path of the Docker provider in a Fleet managed Elastic Agent to be able to use the Docker integration to collect container logs of a Docker rootless setup

### Existing Features

In a Docker rootless setup the Docker sockets usually reside within the users home directory and not under the default "/var/run/docker.sock". For the metrics collection of the integration the socket can be configured. The container_logs dataset seems to rely on variables provided by the Docker provider though. By default the Docker provider has "/var/run/docker.sock" configured as the socket path. As far as I have seen it is not possible to manually configure the providers in a Fleet-managed Elastic Agent setup. It would be necessary to configure the socket path to support any kind of Docker rootless setup.

### What did you see?

There is no way to configure the Docker provider of a Fleet managed Elastic Agent

### Anything else?

The easiest way to implement any way to configure this might be to just respect the DOCKER_HOST environment variable, similarly like it is done with KUBECONFIG in the Kubernetes provider. This way the default behaviour could at least be overridden by manually setting this on a host even if it is not supported through Kibana/Fleet configuration.