WIP: Resolve "Add .npmrc button to project presenter file options"

What does this MR do?

Adds a new Add .npmrc button to the project presenter statistics buttons section. This button will only appear if there is a package.json file at the root level of the project structure (and the user has suitable permissions).

Screenshots

Add Button	New File Page	Once Added (or already existing)

Gif:

Generated file content:

# Add this line for each package scope you want to use GitLab as a registry for, changing <package-scope> to suit your package
@<package-scope>:registry=http://0.0.0.0:3000/api/v4/packages/npm/

# Uncomment the below line if you wish to upload NPM packages to the package registry
# Replace <your_project_id> with the project id of your registry and <your_auth_token> with your auth token
# http://0.0.0.0:3000/api/v4/projects/<your_project_id>/packages/npm/:_authToken=<your_auth_token>

# Replace <your-auth-token> with a user or ci auth token
http://0.0.0.0:3000/api/v4/packages/npm/:_authToken=<your-auth-token>

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #36657