Merge typed role and role group configs

[maltesander]

Description

This PR adds a macro Optional that must be used in the FooConfig(s) of our operators.

# use stackable_operator::config::optional::Optional;
const DEFAULT_PORT: u16 = 11111;
// For example, this:
#[derive(Optional)]
struct FooConfig {
    #[optional(default_value = "DEFAULT_PORT")]
    port: u16,
}
// Expands to (roughly) the following:
#[derive(Merge)]
struct OptionalFooConfig {
    port: Option<u16>,
}
impl From<OptionalFooConfig> for FooConfig {
   fn from(c: OptionalFooConfig) -> Self {
       Self {
           port: c.port.unwrap_or(DEFAULT_PORT),
       }
   }
}

The two created Configs are contained in the CommonConfiguration in an enum like:

pub enum Config<O, M>
where
    O: Clone + Default + Merge,
    M: Configuration + From<O>,
{
    #[serde(rename = "config")]
    Optional(O),
    #[serde(skip)]
    Merged(M),
}

The Optional part representing OptionalFooConfig will be exposed in the CRD. After deserilization and merging the operators work with the Merged part containing the original FooConfig. To retrieve the "original" merged FooConfig in the code, a get method must be called. This is breaking as well as the new Role parametrization:

let port = rolegroup.config.config.get().port;

This means we now need to configure our Role in the FooClusterSpec like:

#[derive(Clone, CustomResource, Debug, Default, Deserialize, JsonSchema, PartialEq, Serialize)]
#[kube(
    group = "foo.stackable.tech",
    version = "v1alpha1",
    kind = "FooCluster",
    plural = "fooclusters",
    shortname = "foo",
    namespaced,
    crates(
        kube_core = "stackable_operator::kube::core",
        k8s_openapi = "stackable_operator::k8s_openapi",
        schemars = "stackable_operator::schemars"
    )
)]
#[serde(rename_all = "camelCase")]
pub struct FooClusterSpec {
   #[serde(default, skip_serializing_if = "Option::is_none")]
    pub foo_server: Option<Role<OptionalFooConfig, FooConfig>>,
}

Additionally, the Role and RoleGroup have a custom deserializer that merges the Role and RoleGroups OptionalFooConfig including the defaults. That means after deserialization no other merging has to be done.

FYI: It works with ZooKeeper, im not fully happy with the created macro which still has some flaws (e.g. the derives of the OptionalFooConfig are currently hardcoded). There are still alot of clones in the code which i wasnt able yet to remove. Additionally, the merge is not working yet for complex structs. They are Optional in the OptionalFooConfig and due to the Merge trait need an impl for Atomic (which basically stops the merge and just takes whatever is behind the option).

@teozkr I really need you to have a look at the general idea/structure and especially the macro :)

Operator implementation: stackabletech/zookeeper-operator#508

fixes: #284

Review Checklist

• Code contains useful comments
• (Integration-)Test cases added (or not applicable)
• Documentation added (or not applicable)
• Changelog updated (or not applicable)
• Cargo.toml only contains references to git tags (not specific commits or branches)

Once the review is done, comment bors r+ (or bors merge) to merge. Further information

[maltesander]

will be handeld with a different approach by @teozkr. Closing for now.