Add list of maintainers and approvers

[arminru]

Hi! I noticed that the maintainers and approvers of OTel Rust are neither listed in https://github.com/open-telemetry/community/blob/main/community-members.md nor here in the repository.

https://github.com/open-telemetry/opentelemetry-rust/blob/ae00d344a918d880c1ab28002a5c907f5d685e0e/CONTRIBUTING.md?plain=1#L124-L126

just links to

https://github.com/open-telemetry/opentelemetry-rust/blob/ae00d344a918d880c1ab28002a5c907f5d685e0e/CODEOWNERS#L1-L5

but users who are not part of the open-telemetry organization don't have access to view who's part of the rust-approvers (or rust-maintainers) team.

Please mention them in one of these places. Thank you!