feat: add getTsMorphProject method

[Julien-R44]

Two things :

• add a getTsMorphProject() method on Codemods class. so that users can make their own codemods as explained in refactor: make project public in CodeTransformer assembler#74

  export async function configure(command: Configure) {
     const codemods = await command.createCodemods()
     const project = await codemods.getTsMorphProject()
   
    // can do whatever I want
     project.getSourceFileOrThrow('file.ts').addImportDeclaration({
       moduleSpecifier: 'ts-morph',
       namedImports: ['Project'],
     })
  }

• Refactoring the Codemods class so as to create just one instance of ts-morph and CodeTransformer. Creating an instance of ts-morph is a costly operation