Add Schema support

[tigrannajaryan]

Problem Statement

The specification recently added the concept of Schema. We need to add a corresponding implementation in the API and SDK.

Proposed Solution

Here is the proposal in the form of draft PRs:

• Tracer API changes: Add schema URL support to Tracer #1889 (Similar changes will be needed for the Meter).
• Resource SDK changes: Add Schema URL support to Resource #1938
• Generate semantic conventions according to specification version: Generate semantic conventions according to specification version #1933

[tigrannajaryan]

@Aneurysm9 @MrAlias I have 3 draft PRs that show the extent of necessary changes. How do you prefer to move forward? Should I now polish each individual PR and merge each as it is ready or you prefer all 3 to be fully cooked and only after that merge all 3 at once?

[Aneurysm9]

I think the draft PRs are already pretty close to mergeable, so polishing them individually would be fine by me.

[MrAlias]

I think the draft PRs are already pretty close to mergeable, so polishing them individually would be fine by me.

Agreed!

I'm okay with merging them separately. We will be sure to hold off releasing until they are all merged.

[MadVikingGod]

With all of these merged can we close this? @Aneurysm9 @MrAlias