Restructure files / packages to move towards a flatter structure

[jlvoiseux]

The Go part of the extension codebase is currently composed of a main.go file and of the following packages:

• extension
• e2e-testing
• logsapi

After a discussion with @stuartnelson3, I think that packages should be restructured to actually separate the core code of the extension from packages bringing additional capabilities. The proposed file structure would look like this:

.
├── cli
├── e2e-testing
│   ├── e2e_test.go
│   └── e2e_util.go
├── lambda-api (former logsapi package, which will also include logic related to the extension api)
│   ├── extension_client.go
│   ├── logs_client.go
│   └── logs_server.go
├── data_forwarder.go (former apm_server.go)
├── data_receiver.go (former route-handlers+http_server.go)
├── events.go (former process_events.go)
├── logger.go
└── main.go