Update packaging builds to accommodate new setuptools tarball naming

The tarballs produced by setuptools now use the 'canonical' package name in the file name, i.e. requests_ecp-<version>.tar.gz instead of requests-ecp-<version>.tar.gz; this PR updates the packaging CI and specifications to accommodate that change.

This change also renames the source RPM package name to python-requests-ecp as per the standard naming convention.