Rename _docker_ vars to _container_ for kakaotalk, telegram, synapse

These three roles have multiple variable prefixes each:
- kakaotalk: matrix_appservice_kakaotalk + matrix_appservice_kakaotalk_node
- telegram: matrix_mautrix_telegram + matrix_mautrix_telegram_lottieconverter
- synapse: matrix_synapse + matrix_synapse_customized + matrix_synapse_rust_synapse_compress_state

For each: renamed _docker_image* to _container_image* (and _docker_src*,
_docker_repo* where applicable), added deprecation entries in
validate_config.yml, updated group_vars references, and moved
deprecation tasks to the front of validate_config.yml.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

roles/custom/matrix-synapse/templates/synapse/ext/s3-storage-provider/bin/migrate.j2

@@ -14,7 +14,7 @@ container_id=$(\
 	{% for arg in matrix_synapse_ext_s3_storage_provider_container_arguments %}
 	{{ arg }} \
 	{% endfor %}
-	{{ matrix_synapse_docker_image_final }} \
+	{{ matrix_synapse_container_image_final }} \
 	-c 's3_media_upload update-db $UPDATE_DB_DURATION && s3_media_upload --no-progress check-deleted $MEDIA_PATH && s3_media_upload --no-progress upload $MEDIA_PATH $BUCKET --delete --storage-class $STORAGE_CLASS --endpoint-url $ENDPOINT {% if matrix_synapse_ext_synapse_s3_storage_provider_config_sse_customer_enabled %}--sse-customer-algo $SSE_CUSTOMER_ALGO --sse-customer-key $SSE_CUSTOMER_KEY{% endif %}' \
 )
 

roles/custom/matrix-synapse/templates/synapse/ext/s3-storage-provider/bin/shell.j2

@@ -13,7 +13,7 @@ container_id=$(\
 	--workdir=/data \
 	--network={{ matrix_synapse_container_network }} \
 	--entrypoint=/bin/bash \
-	{{ matrix_synapse_docker_image_final }} \
+	{{ matrix_synapse_container_image_final }} \
 )
 
 {# We need to connect to the Postgres network, which should be in this list. #}