Restore MiniStack as the default emulator

[Nahuel990]

#161 made Floci the default because it "serves its whole AWS surface on port 4566, so StackPort works against it with AWS_ENDPOINT_URL alone". That is equally true of MiniStack, which is what the default was before, so the stated reason does not separate the two. This restores it.

Two differences that do separate them:

Image size. ministackorg/ministack:1.5.14 is 70.9 MB compressed against 80.6 MB for floci/floci:latest, both read from Docker Hub today.

No hostname variable. MiniStack derives the URLs it returns from the request Host, so a queue created through localhost:4566 reports http://localhost:4566/... and the same queue fetched as ministack:4566 reports http://ministack:4566/.... Nothing to configure, and the same resources resolve from the host and from other containers. The Floci example needs FLOCI_HOSTNAME=floci and then has to document that the host must use a different address than containers do.

StackPort started as a MiniStack dashboard and MiniStack has been the default since, so this is the status quo rather than a new arrangement.

Kept from #161: the docker run Quick Start, which is better than the pip install line it replaced.

[DaviReisVieira]

Thanks for this, and for laying out the reasoning so clearly. You are right that the justification in #161 did not separate the two emulators, and I have taken the docker run Quick Start line and the note about Host-derived URLs into #168.

Where I am landing differently is on removing Floci altogether. The reason StackPort exists as a standalone tool is the direction you and McDoit pushed in ministack#116: talk to any emulator over the standard AWS API, so the whole community can use one browser. Dropping a working example for one of them would go against that, and the same rule that keeps MiniStack's place in the docs has to hold for everyone else.

So #168 restores MiniStack in the root compose, gives both examples the same seed and the same depth, and writes the ground rules down in CONTRIBUTING so this does not depend on anyone's memory. Closing this in favour of #168. Thanks again for catching it and for the PR.