This commit adds copyright attributions in SPDX to the files for matrix-bridge-appservice-kakaotalk following REUSE's specification.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

This commit adds copyright headers to Markdown, YAML, and labels.j2 files. For the rest of the files, which are ones in YAML and JSON files with the extention ".j2", ".license" files are added following the REUSE's specification.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>