feat(capture): Support for "prepend" as field in capture templates

[freddrH]

Summary

In emacs orgmode capture templates can have the property ":prepend". By default captured items are places as the last child (last headline, sub-headline, etc) at the destination. By setting prepend captured items are prepended (placed as the first item at the target) .

Been working with a hack in capture/init.lua locally to have this feature for all templates for myself. Now added the feature to set it in the capture template, as it should be.

Related Issues

Related #

Closes #

Changes

• Added field to capture templates
• target_headline can now have two different outcomes (first and last)

Checklist

I confirm that I have:

• Followed the
  Conventional Commits
  specification (e.g., feat: add new feature, fix: correct bug,
  docs: update documentation).
• My PR title also follows the conventional commits specification.
• Updated relevant documentation, if necessary.
  (starting here as discussed)
• Thoroughly tested my changes.
• Added tests (if applicable) and verified existing tests pass with
  make test.
  (starting here as per discussed, not savvy with testing, looking for pointer)
• Checked for breaking changes and documented them, if any.