*(querylog): added offset/limit parameters

Actually, this is a serious refactoring of the query log module. The
rest API part is refactored, it's now more clear how the search is
conducted. Split the logic into more files and added more tests.

Closes: https://github.com/AdguardTeam/AdGuardHome/issues/1559

openapi/openapi.yaml

@@ -143,13 +143,26 @@ paths:
             tags:
                 - log
             operationId: queryLog
-            summary: Get DNS server query log
+            summary: Get DNS server query log.
             parameters:
                 - name: older_than
                   in: query
                   description: Filter by older than
                   schema:
                       type: string
+                - name: offset
+                  in: query
+                  description:
+                    Specify the ranking number of the first item on the page.
+                    Even though it is possible to use "offset" and "older_than",
+                    we recommend choosing one of them and sticking to it.
+                  schema:
+                      type: integer
+                - name: limit
+                  in: query
+                  description: Limit the number of records to be returned
+                  schema:
+                      type: integer
                 - name: filter_domain
                   in: query
                   description: Filter by domain name