Add new TMT plan and split tests for local and pr-tests

PR-testing and Gating have to test unit-tests based on the installed
package, however, when we are running these tests in local then we want
to start the tests on source and not the installed package.

Create two plans to solve this issue.

Author: jkonecny12

plans/local/basic.fmf

@@ -0,0 +1 @@
+../pr-tests/basic.fmf

plans/local/main.fmf

@@ -0,0 +1,8 @@
+/basic:
+    summary+: ' (localhost)'
+    discover+:
+        filter: tag:local
+    prepare:
+        how: install
+        package:
+            - python3-gobject-base

tests/units/main.fmf

@@ -2,5 +2,15 @@ summary: Run unit tests
 description: Run all unit tests for the Simpleline project.
 contact: Jiri Konecny <[email protected]>
 duration: 10m
-path: tests/
-test: ./units/run_test.sh
+
+/source:
+    summary+: ' (source)'
+    path: /
+    test: ./tests/units/run_test.sh
+    tag: local
+
+/system:
+    summary+: ' (system)'
+    path: tests/
+    test: ./units/run_test.sh
+    tag: sys-installed