[Rust] Enhancements to Rust generator

[wing328]

Description

Here is a list of enhancements I can think of for the Rust client generator:

• Add "docstring" to methods in API and model files for documenting the usage
• Add support for form parameters
• Add support for file upload (type: file)
• Add validation for parameters and model properties
• Make timeout (http) configurable
• Implement 'object' type conversion ([Rust] Implement 'object' type conversion #6846)

If anyone has any feedback/suggestion, please reply to let us know.

Swagger-codegen version

Latest master

Command line used for generation

mvn clean install
java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate  -t modules/swagger-codegen/src/main/resources/rust -i modules/swagger-codegen/src/test/resources/2_0/petstore.yaml -l rust -o samples/client/petstore/rust

Related issues/PRs

#6105

If anyone wants to work on these enhancements, please reply to let us know and we'll show you some good starting points.

[wing328]

Minor fix for Windows platform via cc848a1

[wing328]

Added "Implement 'object' type conversion" via #6846