RouDi modularisation

## Brief feature description

The current modules and classes in RouDi are entangled and sometimes depend on each other. For safety certification a clear structure and concept is needed.

## Detailed information

* [ ] Replace `m_run` in `CmdLineArgs_t`, also see [here](https://github.com/eclipse-iceoryx/iceoryx/pull/523#discussion_r569483881)
* [ ] Draft a plan on how to [split](https://github.com/eclipse-iceoryx/iceoryx#targeted-quality-levels--platforms) iceoryx_posh
* [ ] Distinguish between safety and community building blocks
* [ ] `RouDi::monitorAndDiscoveryUpdate()` needs to be removed for static discovery (see [this](https://github.com/eclipse-iceoryx/iceoryx/pull/784#discussion_r633377318) discussion)
* [ ] Create objects in shared memory statically during init phase
* [ ] Implement split of `iceoryx_posh`
* [ ] `ProcessManager::ProcessManager` shall use separate error codes for each error
* [ ] Move RouDI into separate CMake target
* [ ] Move namespace `roudi` contents from `iceoryx_posh_types.hpp` into roudi cmake target