Allow resolving from resolved schema using Manifest file.

[jsuereth]

Fixes #1134

Should allow specifying a schema like in OTEP 4815.

• Can specify a manifest instead of a directory, e.g. http://my-schema.org/manifest/1.0.0
• Will use the resolved_schema_url, if available, on that manifest to resolve schema instead of grabbing .yaml files from the directory.
• Allow relative URLs for resolved_schema_url, although this needs to be tested a bit.

Thing not working yet:

• Extending groups from V2
• Actually using manifest.yaml vs. registry_manifest.yaml as per OTEP 4815.

[codecov]

Codecov Report

❌ Patch coverage is 84.83607% with 37 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.4%. Comparing base (a74480e) to head (a18e5a6).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/weaver_resolver/src/dependency.rs	89.3%	17 Missing ⚠️
crates/weaver_resolver/src/loader.rs	70.0%	9 Missing ⚠️
crates/weaver_common/src/vdir.rs	46.1%	7 Missing ⚠️
crates/weaver_common/src/lib.rs	75.0%	2 Missing ⚠️
crates/weaver_resolver/src/attribute.rs	94.7%	1 Missing ⚠️
crates/weaver_semconv/src/registry_repo.rs	93.3%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1160     +/-   ##
=======================================
+ Coverage   80.1%   80.4%   +0.3%     
=======================================
  Files        108     108             
  Lines       8440    8661    +221     
=======================================
+ Hits        6763    6967    +204     
- Misses      1677    1694     +17     

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