add initial codeowners file for repo on tool basis

CODEOWNERS

+# UNICADO Codeowners - tool specific ownership
+
+# Design tools
+create_mission_xml/           @gPauls-TUHH
+empennage_design/             @ChrisRuw         @AndiGob
+fuselage_design/              @AndiGob
+initial_sizing/               @ellen.seabrooke  @johannes.schneider
+landing_gear_design/          @AndiGob
+propulsion_design/            @tobi747          @kristina.mazur       @meric.taneri       @alfinjohny1
+systems_design/               @ellen.seabrooke
+tank_design/                  @s-roscher
+wing_design/                  @ChrisRuw
+
+# Analysis tools
+aerodynamic_analysis/         @lukas.neuerburg  @Florian.Schueltke
+mission_analysis/             @kbistreck        @gPauls-TUHH
+weight_and_balance_analysis/  @timi97tp         @ChrisRuw
+
+# Assessment tools
+cost_estimation/              @s-roscher
+ecological_assessment/        @kbistreck
+flight_mechanic_assessment/   @ChrisRuw
+performance_assessment/       @philipp.hansmann