mkt: add slack chat banner (#2266)

* mkt: add slack chat banner

* remove empty space from image

* add banner in other places

* fix image url

Author: alerizzo

Diff for: docs/getting-started/codacy-quickstart.md

@@ -7,6 +7,8 @@ nav_step: 0
 
 Codacy is an automated code quality and coverage platform that analyzes your source code and identifies issues as you go, helping your team ship robust software by scanning over 40 programming languages, such as JavaScript, Python, Java, C#, and PHP.
 
+[![Start Slack chat](./images/slack-banner-2x.png)](https://start-chat.com/slack/codacy/tKNKyy)
+
 Check out our product demo for an overview of Codacy's main features (recorded on May 13, 2024):
 
 <div style="position: relative; padding-bottom: 61.224489795918366%; height: 0;"><iframe src="https://www.loom.com/embed/1ed27d66b659427883ddd28e57468c22" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen style="position: absolute; top: 0; left: 0; width: 100%; height: 100%;"></iframe></div>

Diff for: docs/getting-started/images/slack-banner-2x.png

@@ -1,5 +1,7 @@
 # Changing your plan and billing
 
+[![Start Slack chat](../getting-started/images/slack-banner-2x.png)](https://start-chat.com/slack/codacy/tKNKyy)
+
 Each organization on Codacy has a dedicated plan and associated billing. To make changes to the plan and billing of an organization, open your organization **Settings**, page **Plan and billing**.
 
 <!--plan-caveats-start-->