test: refactor/simplify container mock builders

[piksel]

This PR replaces the mockContainerWith* helpers with a compositable MockContainer function that takes an arbitrary number of updates that mutate the mocked container.
This makes it much easier to combine those parts of the container state that needs to be mocked instead of creating new specialized helpers.

Example usage:

mockContainer := MockContainer(
	WithImageName("docker.io/prefix/imagename:latest"),
	WithLabels(map[string]string{ "com.centurylinklabs.watchtower.enable": "true" }),
	WithPortBindings("80/tcp"),
)

[codecov]

Codecov Report

Base: 64.76% // Head: 64.76% // No change to project coverage 👍

Coverage data is based on head (e3543ce) compared to base (d5d711b).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1495   +/-   ##
=======================================
  Coverage   64.76%   64.76%           
=======================================
  Files          24       24           
  Lines        2310     2310           
=======================================
  Hits         1496     1496           
  Misses        718      718           
  Partials       96       96           

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