Duplicated service description entries within gateway config toml file should not result in duplication of service entries

## Required information

**Operating system:**
Iceoryx Enviroments Linux / QNX

**Compiler version:**
Normal Iceoryx build setup

**Observed result or behaviour:**
If the gateway config toml file has duplicated service descriptions the parser doesnt validates this and creates duplicated service description entries

**Expected result or behaviour:**
The parser should validate this and service entry duplication should not happen

**Conditions where it occurred / Performed steps:**
Ex:

```
serviceEntry->insert("service", "service");
serviceEntry->insert("instance", "instance");
serviceEntry->insert("event", "event");

serviceEntry->insert("service", "service");
serviceEntry->insert("instance", "instance");
serviceEntry->insert("event", "event");
```