Restructure Parser Packages and Rename devfile/parser

[adisky]

Is your task related to a problem? Please describe.

As the current code is imported from odo, It is following the same structure here

if we want to consume the parser functions, we need to do import github.com/devfile/parser/pkg/devfile/parser which looks redundant.

Describe the solution you'd like

• Rename devfile/parser to devfile/library
  devfile/parser ----> `devfile/library

• Reconsider the structure, a rough idea

devfile/library
- pkg/                   // all we want to expose as library
     - parser/
     - validate/
     - generator/
     - utils/
- tests/
- utils/                // internal utils
- vendor/

[github-actions]

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