Define SemConv predefined JQ functions

[lquerel]

This PR adds a set of predefined JQ functions to simplify the processing and generation of semconv documentation/code.

Process Registry Attributes

The following JQ filter extracts the registry attributes from the resolved registry and returns a list of registry attributes grouped by namespace and sorted by attribute names.

templates:
  - pattern: attributes.j2
    filter: semconv_grouped_attributes
    application_mode: each

The output of the JQ filter has the following structure:

[
  {
    "root_namespace": "user_agent",
    "attributes": [
      {
        "brief": "Value of the HTTP User-Agent",
        "examples": [ ... ],
        "name": "user_agent.original",
        "root_namespace": "user_agent",
        "requirement_level": "recommended",
        "stability": "stable",
        "type": "string",
        // ... other fields
      }, 
      // ... other attributes in the same root namespace
    ]
  },
  // ... other root namespaces
]

The semconv_grouped_attributes function also supports options to exclude specified root namespaces, specific stability levels, and deprecated entities. The following syntax is supported:

templates:
  - pattern: attributes.j2
    filter: >
      semconv_grouped_attributes({
        "exclude_root_namespace": ["url", "network"], 
        "exclude_stability": ["experimental"],
        "exclude_deprecated": true,
      })
    application_mode: each

The structure of the output of semconv_grouped_attributes with these options is exactly the same as without the options. The JSON object passed as a parameter describes a series of options that can easily be extended if needed. Each of these options is optional. It's also possible to use the special parameter $params as follows:

params:
  exclude_root_namespace: ["url", "network"] 
  exclude_stability: ["experimental"]
  exclude_deprecated: true

templates:
  - pattern: attributes.j2
    filter: semconv_grouped_attributes($params)
    application_mode: each

Technically, the semconv_grouped_attributes function is a combination of two semconv JQ functions:

def semconv_grouped_attributes($options):
    semconv_attributes($options)
    | semconv_group_attributes_by_root_namespace;

def semconv_grouped_attributes: semconv_grouped_attributes({});

The semconv_attributes function extracts the registry attributes and applies the given options. The semconv_group_attributes_by_root_namespace function groups the attributes by root namespace. It's possible to combine these two functions with your own JQ filters if needed.

Process Metrics

The following JQ filter extracts the metrics from the resolved registry, sorted by group root namespace and sorted by metric names.

templates:
  - pattern: metrics.j2
    filter: semconv_grouped_metrics
    application_mode: each

The output of the JQ filter has the following structure:

[
  {
    "root_namespace": "jvm",
    "metrics": [
      {
        "attributes": [ ... ],
        "brief": "Recent CPU utilization for the process as reported by the JVM.",
        "id": "metric.jvm.cpu.recent_utilization",
        "instrument": "gauge",
        "metric_name": "jvm.cpu.recent_utilization",
        "root_namespace": "jvm",
        "note": "The value range is [0.0,1.0]. ...",
        "stability": "stable",
        "type": "metric",
        "unit": "1",
        // ... other fields
      },
      // ... other metrics in the same root namespace
    ]
  },
  // ... other root namespaces
]

The same options are supported by semconv_grouped_metrics, as shown in the following example:

params:
  exclude_root_namespace: ["url", "network"] 
  exclude_stability: ["experimental"]
  exclude_deprecated: true

templates:
  - pattern: metrics.j2
    filter: semconv_grouped_metrics($params)
    application_mode: each

All the semconv_grouped_<...> functions are the composition of two functions: semconv_<...> and semconv_group_<...>_by_root_namespace.

Other improvements

This PR contains an update of the Weaver Forge README.md.
This PR updates the Rust example to leverage both the whitespace control settings and the new JQ filters.

[jsuereth]

Overall LGTM. Just called out some of my concerns going forward on formalizing semconv decisions over here in the weaver codebase.

[lmolkova]

Could we postpone adding semconv_grouped_resources, semconv_grouped_scopes, semconv_grouped_spans, semconv_grouped_events until we have a use-case?

[lmolkova]

Left some minor comments, looks great otherwise!

[lquerel]

@lmolkova, @jsuereth, once I get confirmation for the few questions I have (see previous comment), I will make the changes, bump the weaver version, and create a new release. This release will be a good starting point for the codegen authors as these new JQ filters improve the UX. The step-by-step guide should also ease the process of the codegen migration.