Fixes #1687

Changes

This PR lays out the initial structure of the semantic conventions for mainframes.

The PR adds the following new components to the semantic conventions:

1. mainframe: Adds single attribute to registry right now, (planned for platform-specific definitions moving forward)
2. zos: Adds z/OS related attributes and definition of z/OS system software resource (zos.software)
3. tps: Introduces new (generic) Transaction Processing System (TPS), an initial set of attributes and defines TPS spans extending the HTTP and RPC servers spans, and uses them for initial definition of server spans for the TPS CICS and IMS available on the mainframe.

The PR is based on the input from the Mainframe SIG meetings and is intended to have the discussion to complete the definition of a generic Transaction Processing System and to determine how mainframe concepts will be integrated in the semantic conventions. Basing on the generic TPS, we aim to finalize the span definitions for CICS and IMS.

Note

Note: if the PR is touching an area that is not listed in the existing areas, or the area does not have sufficient domain experts coverage, the PR might be tagged as experts needed and move slowly until experts are identified.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.