Add support for annotations on attributes and groups

[lquerel]

See open-telemetry/semantic-conventions#1462 (comment) for more context.

This PR adds an annotations field to the definition of attributes and groups. In this initial iteration, annotations are opaque to Weaver and represented as a key→YAML-value map.

Annotations become accessible, after registry resolution, within JQ expressions, Jinja templates, and the Rego engine.

In the future, we may introduce a new group type allowing users to define the structure of annotations directly within the semconv registry.

[codecov]

Codecov Report

Attention: Patch coverage is 44.15584% with 43 lines in your changes missing coverage. Please review.

Project coverage is 73.7%. Comparing base (0316b08) to head (0b307df).

Files with missing lines	Patch %	Lines
crates/weaver_semconv/src/lib.rs	33.3%	42 Missing ⚠️
crates/weaver_resolved_schema/src/lineage.rs	88.8%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #645     +/-   ##
=======================================
- Coverage   74.2%   73.7%   -0.5%     
=======================================
  Files         57      57             
  Lines       4578    4655     +77     
=======================================
+ Hits        3399    3433     +34     
- Misses      1179    1222     +43     

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[lmolkova]

Schema changes look good to me!

(Rust code too, but I'm not qualified)

[jerbly]

LGTM