Hardcoded creation date-time replaced by attribute "docprodtime"

[larsbarring]

N.B. Requires updates to the github workflow as suggested below.

See issue #457 for discussion of the changes.

Release checklist

• [ NA] Authors updated in cf-conventions.adoc?
• [ NA] Next version in cf-conventions.adoc up to date? Versioning inspired by SemVer.
• [yes] history.adoc up to date?
• [ NA] Conformance document up-to-date?

For maintainers

After the merge remember to delete the source branch.
Tags are set at the conclusion of the annual meeting; until then master always is a draft for the next version.

Replacing the hardcoded document creation date with an AsciiDoc attribute (with more flexible formatting than the builtin {localdatetime}) requires the format specification attribute to be set at the command line. The code changes below have not been tested in a github workflow, but the corresponding shell commands works when run locally.

... 
...
 - name: Set draft date-time formatting       ## new
      if github.event_name != 'release'       ## new
      run: |       ## new
        echo "DATE_FMT='+%d %B, %Y %H:%M:%SZ'" >> "$GITHUB_ENV"       ## new
 - name: Set "final" tag and date-time formatting       ## changed
      if: github.event_name == 'release'
      run: |
        echo "FINAL_TAG=-a final" >> "$GITHUB_ENV"; echo "DATE_FMT='+%d %B, %Y'" >> "$GITHUB_ENV"       ## changed
    # Build cf-conventions.html using the Analog-inc asciidoctor-action
    - name: Build cf-conventions.html
      uses: Analog-inc/[email protected]
      with:
        shellcommand: 'asciidoctor --verbose ${FINAL_TAG} -a docprodtime="$(date -u ${DATE_FMT})" cf-conventions.adoc -D conventions_build; cp -r images conventions_build'      ## changed
    # Build cf-conventions.pdf using the Analog-inc asciidoctor-action
    - name: Build cf-conventions.pdf
      uses: Analog-inc/[email protected]
      with:
        shellcommand: 'asciidoctor-pdf --verbose ${FINAL_TAG} -a docprodtime="$(date -u ${DATE_FMT})" -d book cf-conventions.adoc -D conventions_build'       ## changed
    # Upload artifact containing cf-conventions.html, cf-conventions.pdf

Could possibly someone from the Information Management and Support Team have a look at this?
ping e.g. @DocOtak, @sadielbartholomew, @cofinoa, @davidhassell

[larsbarring]

I am closing this PR, but will shortly open a new one that includes the suggested changes to the workflow.