Move sync behaviour from common to own package

[Integralist]

Problem: I'm increasingly stumbling into issues with the common package being too broad/generic. This materialises as an "import cycle error". It is also considered bad practice to have folders named common or utils etc.
Solution: Move these behaviours into their own packages.
Example: I would like to add a remediation error type to some code in our config package. This isn't possible because importing the errors package will import text which will import common and the common package has already been imported earlier in the import cycle:

package github.com/fastly/cli/cmd/fastly
        imports github.com/fastly/cli/pkg/app
        imports github.com/fastly/cli/pkg/backend
        imports github.com/fastly/cli/pkg/common << command stuff like: Base/Register/StreamingExec + lots more other misc stuff.
        imports github.com/fastly/cli/pkg/config
        imports github.com/fastly/cli/pkg/errors
        imports github.com/fastly/cli/pkg/text
        imports github.com/fastly/cli/pkg/common: import cycle not allowed

[fgsch]

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