chore: always close Docker client

[mdelapenya]

What does this PR do?

This PR improves how the Docker client is handled:

• it simplifies how the API version is negotiated when retrieving a Docker client: instead of forcing a call to the NegotiateAPIVersion(ctx) method, it's passed as a client Opt when getting the new client.
• it unifies how a Docker client is retrieved, creating an internal function to it. There, we will centralise the creation of the Docker client.
• it also adds a Close method to the DockerProvider struct. With it, we have identified the usages of the DockerProvider, and its underlying Docker client, to close the client and avoid leaking Docker connections.

As part of the PR we are moving the provider related code to a separate Go file, and identified that all compose_test.go paths were not using filepath to create cross-OS paths.

Why is it important?

It makes sure that we are not leaking Docker client connections, making sure it's closed everywhere, also providing a way to close the Docker Provider wrapper.

Related issues

• Closes Docker connection not closed #321

Follow-ups

@Eun I'm not adding the test you provided in the original issue because I dit not see any difference running it against this branch or main (without the closes). Do you think we must add them to be covered? My only concern would be plugin the leak detector to the TestMain (goleak.VerifyTestMain(m), see https://pkg.go.dev/go.uber.org/goleak#readme-quick-start):

Instead of checking for leaks at the end of every test, goleak can also be run at the end of every test package by creating a TestMain function for your package.

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[Eun]

I don't think adding my tests would help, I just added them to have a fast reproducible result.
However since this is not reproducible at all (anymore), I would not bother with tests at the moment.

so LGTM from my side.

As a side note:
the goleak package was changed, so it doesn't produce the output anymore.
Maybe its worth checking the options available or using an older version of goleak to reproduce the issue at least once and see that it is resolved.