Feature/graph manager (#38)

* Initial changes

* Working state

* Working state

* Working state

* Working state

* Working state

* Working state

* Added graph listener

* Updates

* Testing name demangling

* Graph manager: reworked

* Remove debug trace

* Treat errors when freeing rcutils resources

* Improve logics for discovering entities

* Working state: Micro-ROS graph manager

* Fix micro_ros_graph_info typesupport type name

* Remove double CMakeLists comment

* Remove package.xml commented block

* Add missing include

* Added CI

* Remove GUID_t param from callbacks signature

* Add services names and types to micro-ROS graph topic

* Differenciate between service server and clients

* remove debug traces

Co-authored-by: Pablo Garrido <pablogs9@gmail.com>

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behaviour:
+1. Clone repo '...'
+2. Add these lines '...'
+3. Run the script '....'
+4. See error
+Code or shell commands ready to be copy-pasted are welcome.
+
+**Expected behaviour**
+A clear and concise description of what you expected to happen.
+
+**System information (please complete the following information):**
+ - OS: [e.g. WIndows 10, Ubuntu 16.04, ...]
+ - ROS 2 [e.g. Dashing, Foxy, ...]
+ - Version [e.g. commit hash, tag, ...]
+
+**Additional context**
+Add any other context about the problem here.

.github/workflows/ci.yml

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+name: CI micro-ROS Agent
+
+on:
+    pull_request:
+      branches: 
+        - '**'
+
+jobs:
+
+    microros_agent_ci:
+        runs-on: ubuntu-20.04
+        container: ros:foxy
+    
+        steps:
+        - uses: actions/checkout@v2
+          with:
+            path: src/micro_ros_agent
+
+        - name: Download dependencies
+          run: |
+            git clone -b foxy https://github.com/eProsima/Micro-XRCE-DDS-Agent src/microxrcedds_agent
+      
+        - name: Build
+          run:  |
+            . /opt/ros/foxy/setup.sh
+            colcon build