MQTT wildcard and prefix fix

[Woestebanaan]

Previously, the $ wildcard in KCQL target mappings only worked as a standalone value — getTarget had to return exactly "$" for the MQTT source topic to be used as the target. If a user wrote something like "prefix_$" or "data/$_events", the $ would not be substituted and the literal string (including $) would be used as-is.

This change adds support for $ as an embedded placeholder within a larger target string. The sanitized MQTT topic name is now substituted wherever $ appears in the target.

Examples:

KCQL Target	MQTT Topic	Before	After
$	/sensor/temp	sensor_temp	sensor_temp
prefix_$	/sensor/temp	prefix_$	prefix_sensor_temp
data/$_events	/sensor/temp	data/$_events	data/sensor_temp_events

Also fixed the single and multi-level MQTT wildcards

Resolved the following issue: #1386