OZG-7707 replace more icons

...tion-mapping-form/aggregation-mapping-form.component.html

...n-mapping-form/aggregation-mapping-form.component.spec.ts

...gation-mapping-form/aggregation-mapping-form.component.ts

alfa-client/libs/design-system/src/index.ts

...lib/icons/orga-unit-icon/orga-unit-icon.component.spec.ts

.../src/lib/icons/orga-unit-icon/orga-unit-icon.component.ts

...em/src/lib/icons/orga-unit-icon/orga-unit-icon.stories.ts

...ystem/src/lib/icons/plus-icon/plus-icon.component.spec.ts

...ign-system/src/lib/icons/plus-icon/plus-icon.component.ts

...esign-system/src/lib/icons/plus-icon/plus-icon.stories.ts

.../postfach-mail-button/postfach-mail-button.component.html

...stfach-mail-button/postfach-mail-button.component.spec.ts

alfa-client/libs/postfach/src/lib/postfach.module.ts

...-create-button/wiedervorlage-create-button.component.html

...eate-button/wiedervorlage-create-button.component.spec.ts

...client/libs/wiedervorlage/src/lib/wiedervorlage.module.ts