[typescript-angular] service configuration/basePath modification after construction

[macjohnny]

Description

See original issue here: swagger-api/swagger-codegen#7949

openapi-generator version

3.0.0

[macjohnny]

@chrismellard @akehir would you like to add your PR swagger-api/swagger-codegen#8305 here at OpenAPI Generator (a community fork of swagger codegen)? it should be easy to migrate the code, simply rename the files and you are done.