Remove unnecessary explicit dependencies from the core Rollbar module and two new optional SDK modules

[akornich]

Description of the change

• resolve GH#577 - Remove unnecessary explicit dependencies from the core Rollbar module
• resolve GH#576 - Move appsettings.json support into its own new module Rollbar.AppSettings.Json
• resolve GH#575 - Move app.config support into its own new module Rollbar.App.Config

Namespace Rollbar.NetFramework is renamed into Rollbar.App.Config and moved to the similarly named new optional SDK module.

Namespace Rollbar.NetCore is renamed into Rollbar.AppSettings.Json and moved to the similarly named new optional SDK module.

A few unit tests moved to new dedicated unit test projects. A couple of new unit tests added.

It also includes 2 new sample apps to separately demonstrate the use of each of the new SDK modules. Some of the existing samples had to be updated to adapt to this refactoring effort. Some small code cleanup as needed while refactoring.

Type of change

• [ ] Bug fix (non-breaking change that fixes an issue)
• [ ] New feature (non-breaking change that adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Related issues

Implement #577 Implement #576 Implement #575

Checklists

Development

• [x] Lint rules pass locally
• [x] The code changed/added as part of this pull request has been covered with tests
• [x] All tests related to the changed code pass in development

Code review

• [ ] This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached
• [ ] "Ready for review" label attached to the PR and reviewers mentioned in a comment
• [ ] Changes have been reviewed by at least one other engineer
• [ ] Issue from task tracker has a link to this pull request

[akornich]

@bishopb , thanks for the prompt review!