Dockerfile label updates, change version string in RELEASE.txt

LABELS now use ci standard opencontainers naming for:

 vendor, description and version

annotations. In version, source value was removed and source moved to
description.  Added annotations for:

  title
  licenses
  documentation

licenses includes Python-2.0 license in preparation for vendoring cgi
and cgitb modules in 2.4.0.

Updated RELEASE.txt to include version string in Dockerfile.

Author: rouilj

RELEASE.txt

@@ -34,6 +34,7 @@ Roundup release checklist:
       roundup/__init__.py
       website/www/index.txt (current stable version, release highlights)
       website/www/conf.py  (update copyright, version from __init__.py)
+      scripts/Docker/Docker update value of org.opencontainers.image.version
 3a. Update license end date in COPYING.txt
 3b. Update doc/acknowledgements.txt (add section for
     release, churn contributers etc.). (Use hg churn -c -r ####..####)

scripts/Docker/Dockerfile

@@ -195,10 +195,14 @@ RUN apk --no-cache upgrade; \
     fi
 
 ARG source
-LABEL "org.roundup-tracker.vendor"="Roundup Issue Tracker Team" \
-      "org.roundup-tracker.description"="Roundup Issue Tracker multi-backend" \
-      "version"="2.2.0 $source" \
-      "org.opencontainers.image.authors"="[email protected]"
+LABEL "org.opencontainers.image.vendor"="Roundup Issue Tracker Team" \
+      "org.opencontainers.image.title"="Roundup Issue Tracker" \
+      "org.opencontainers.image.description"="Roundup Issue Tracker with multi-backend support installed via $source" \
+      "org.opencontainers.image.version"="2.2.0" \
+      "org.opencontainers.image.authors"="[email protected]" \
+      "org.opencontainers.image.licenses"="MIT AND ZPL-2.0 AND Python-2.0"
+      "org.opencontainers.image.documentation"="https://www.roundup-tracker.org/docs/installation.html"
+
 
 ARG pythonversion
 # pull over built assets