Issue #230: Document SQL Source and add module entry in README

Added documentation for SQL Source and added module entry in README

README.md

@@ -18,6 +18,7 @@ This is a multi-module project:
 * **metricshub-snmp-extension-common**: Contains common functionalities and utilities used by SNMP-based extensions.
 * **metricshub-snmp-extension**: Enables Simple Network Management Protocol (SNMP) for monitoring and managing network devices.
 * **metricshub-snmpv3-extension**: Adds support for SNMPv3, which includes enhanced security features like authentication and encryption.
+* **metricshub-sql-h2-source-extension**:  Allows execution of SQL queries on already existing sources.
 * **metricshub-win-extension-common**: Contains common functionalities and utilities used by Windows-specific extensions.
 * **metricshub-wmi-extension**: Provides support for Windows Management Instrumentation (WMI) to gather detailed information about Windows systems.
 * **metricshub-winrm-extension**: Enables the use of Windows Remote Management (WinRM) for remote management and monitoring of Windows-based systems.

metricshub-doc/src/site/markdown/develop/connector.md

@@ -329,6 +329,19 @@ monitors:
               concatStart: # <string>
               concatEnd: # <string>
           computes: <compute-object-array>
+        # SQL Source
+        <sql-sourceKey>: # <source-object>
+        <sourceKey>:
+          type: sql
+          tables: <sqltable-object-array>
+          - source: <string>
+            alias: <string>
+            columns: <sqlcolumn-object-array>
+            - name: <string>
+              number: <integer>
+              type: <string>
+          query: <string>
+          computes: <compute-object-array>
 
         # Computes
         <sourceKey>: # <source-object>

metricshub-doc/src/site/markdown/develop/sources/sql.md

@@ -0,0 +1,28 @@
+keywords: sql, h2, database
+description: The SQL source allows to perform SQL queries on other Sources.
+
+# SNMP Get (Source)
+
+```yaml
+connector:
+  # ...
+pre: # <object>
+  <sourceKey>: # <source-object>
+
+monitors:
+  <monitorType>: # <object>
+    <job>: # <object>
+      sources: # <object>
+        <sourceKey>:
+          type: sql
+          tables: <sqltable-object-array>
+          - source: <string>
+            alias: <string>
+            columns: <sqlcolumn-object-array>
+            - name: <string>
+              number: <integer>
+              type: <string>
+          query: <string>
+          computes: <compute-object-array>
+```
+

metricshub-doc/src/site/site.xml

@@ -126,6 +126,7 @@
 				<item name="WMI" href="develop/sources/wmi.html" />
 				<item name="Static (Constant)" href="develop/sources/static.html" />
 				<item name="Copy (Duplicate)" href="develop/sources/copy.html" />
+				<item name="SQL" href="develop/sources/sql.html" />
 				<item name="Pre-Sources" href="develop/sources/pre.html" />
 			</item>
 			<item name="Computes" href="develop/computes/index.html" >