Rename Ruby packaging scripts (libddprof to libdatadog) and package 0.7.0-rc.1 release for Ruby

[ivoanjo]

What does this PR do?

• Rename Ruby packaging scripts (libddprof to libdatadog)
• Package 0.7.0-rc.1 release for Ruby

Motivation

Use libdatadog in dd-trace-rb

Additional Notes

Since this was the first release, as an exception, I've already pushed it on rubygems.org (https://rubygems.org/gems/libdatadog) to reserve the name for our use.

How to test the change?

1. Check the new release hashes match those on https://github.com/DataDog/libdatadog/releases/tag/v0.7.0-rc.1
2. Validate release shows up on https://rubygems.org/gems/libdatadog
3. Observe that CI is green in this downstream dd-trace-rb PR that picks up this new version for use Replace libddprof dependency with libdatadog, and upgrade to 0.7.0 dd-trace-rb#2061

[pawelchcki]

Thanks @ivoanjo ! Looks good to me!