tpl/tplimpl: Update schema template

tpl/tplimpl: Update schema template

Changes:

- Remove trailing comma from list of keywords.
- Improve keywords precedence:
  1. Use "keywords" term page titles.
  2. Use "keywords" from front matter if "keywords" is not a taxonomy.
  3. Use "tags" term page titles.
  4. Use term page titles from all taxonomies.
- Enable schema for all page kinds, previously limited to kind = page.
- Remove trailing slashes from void elements.
- Improve readability.

Closes #7570

Co-authored by: 0urobor0s <0urobor0s@users.noreply.github.com>