Design modules startup sequence

[softgitron]

Describe the supposed addition
Module's and core's API calls are unambiguously defined as can be seen in the PR #11. However API specification does not specify how the module's startup sequence is handled. This detail should be designed and startup sequence diagram should be added into the wiki.

My initial proposal for the startup sequence is following, but can be altered if actual implementer of this issue founds better solution.

1. Core reads modules manifest files (capabilities and OpenAPI specifications)
2. Core starts module process with following environment variables

• CORE_TOKEN=ey... *
• MODULE_TOKEN=ABC123... **

3. Core sends X-amount of health check requests on Y interval
4. If the module responds to the health check request, core decides that module has been successfully started
5. After that core may register port triggers on service if needed
6. Handshake is now completed

*CORE_TOKEN is supplied by the module, when sending requests for the core
**MODULE_TOKE is supplied by the core, when sending requests for the module
By utilizing this double token logic, no other module should be able to interfere with the communication.

Pitch your addition with a user story
As a developer I can understand startup sequence between core and module, so that I can implement the startup sequence later on.

Name of the files or sections to be added
Add this under architecture section in the Wiki and add mention of this page into module creation instructions (See issue #22).

Additional context
Issue #22