Initial release of weaver for semantic conventions

Initial release of OpenTelemetry weaver for usage in semantic-conventions repository.

This is a PREVIEW release, and stability guarantees are loose prior to 1.0.

What's Changed:

1. The Weaver project, initially hosted by F5, has been moved to open-telemetry/weaver. The project's objectives have been redefined into two main phases/focuses: 1) semconv support, 2) application telemetry support.
2. A Jinja-compatible template engine and a snippet-based generator have been completed and tested to support the semantic-convention repository. The template engine can be used for both documentation and code generation.
3. A new policy engine (based on rego) has been added to the project to externalize the declaration of policies and to enhance the management, evolution, and maintainability of semantic conventions and application telemetry schemas. It leverages a set of rules or policies to ensure the coherence and quality of these conventions and schemas over time.
4. A lot of documentation has been added to the entire project to make it easier to consume and contribute.
5. A code coverage process has been implemented with the initial goal of keeping the project above 70% coverage.
6. A process for cleaning up APIs has been initiated in anticipation of publishing the crates on crates.io. The weaver_semconv crate is the first to undergo this process.