This PR implements a new subcommand `doc` that generates markdown documentation for a given gRPC service!
**Description**
For the most part, the inner logic of this subcommand is the same as the `describe`, the only thing that changes is the way that the found descriptor is transformed to a final output.
In this case, a `Packages` type has been implemented to transform a `ServiceDescriptor` into a map of `Package`s.
Each package groups all the file descriptors with the same package name (or namespace).
A `Package` contains all the necessary information for a file of documentation to be generated (All its contained services, messages and enum descriptors and its name).
The output of this command is a folder with all the generated documentation, which contains a file per protobuf package.
**Introduced the `granc-test-support` crate**
* Renamed the `echo_service` crate as `granc-test-support`, providing both the definition of a protobuf service for integration testing and a function to compile protobuffer at runtime into a file descriptor (Potentially this could be used to let users pass a folder to a proto project in addition to the server reflection and the local file descriptor options. For example, the `call` command could compile a file descriptor on the fly from a folder containing a protobuffer project before making the call to the gRPC server.
**Descriptor API Enhancements:**
* Added `name`, `full_name`, and `package_name` methods to the `Descriptor` enum to simplify access to descriptor metadata. (`granc-core/src/client/types.rs`)
**Dependency Management Improvements:**
* Added grouping for gRPC-related dependencies in `dependabot.yml` for improved automated dependency updates. (`.github/dependabot.yml`)
