feat(data-index): generator + Cimas fixes for relaton-data-* Pages rollout

[andrew2net]

What

Adds a source-of-truth generator for the per-repo GitHub Pages index _config.yml of the remaining relaton-data-* repos (relaton/relaton#48), and fixes the Cimas plumbing so the deploy workflow actually reaches them.

Storage split (matches how oasis/w3c/ids already work): unique _config.yml is repo-owned, generated from a single table here; identical plumbing (deploy.yml, Gemfile.deploy) stays Cimas-managed.

Changes

• data-index/configs.yml + bin/gen-data-index-config — render each repo's _config.yml with verified source (published INDEXFILE), baseurl (real default branch), and pubid_class. lib/ + spec/ + Gemfile/Rakefile add an rspec harness (repo had none).
• cimas-config/cimas.yml — correct stale branch: fields to real defaults (20 repos moved to v2); add adobe/easc/gost/jcgm/oiml; remove the duplicate relaton-data-cie key; add iso to the data group; give jis its deploy.yml.
• cimas-config/gh-actions/data/deploy.yml — trigger on [master, main, v2] + pull_request so v2-default repos publish (the reusable data-deploy.yml still gates deploy on the default branch).
• data-index/README.adoc — rollout runbook + rendering-readiness tiers.

Rendering readiness

Verified against the published indexes:

• Renders today (string ids): 3gpp, ogc, xsf, rfcs, rfcsubseries, calconnect, iana.
• Builds, raw-hash rows: bipm, ecma.
• Needs a theme fix (external-pubid _type hashes): the 16 pubid_class flavors — the theme plugin currently calls klass.new(**id), but those classes are modules (.create is the right call). Tracked separately for relaton/jekyll-theme-relaton-data-index.

Tests

bundle exec rake → 11 examples, 0 failures. All changed YAML parses; cimas.yml structural checks pass; all 25 configs render valid.

Notes

• Base is main (where the default-branch-gated data-deploy.yml@main the master references lives).
• Pre-existing, out-of-scope bugs spotted in cimas.yml and left untouched: relaton-model-etsi remote points at relaton-model-ccsds; all relaton-model-* have empty files:.