chore: using bitly to manage expiring Slack invitation links (#22631)

README.md

@@ -25,7 +25,7 @@ under the License.
 [![PyPI version](https://badge.fury.io/py/apache-superset.svg)](https://badge.fury.io/py/apache-superset)
 [![Coverage Status](https://codecov.io/github/apache/superset/coverage.svg?branch=master)](https://codecov.io/github/apache/superset)
 [![PyPI](https://img.shields.io/pypi/pyversions/apache-superset.svg?maxAge=2592000)](https://pypi.python.org/pypi/apache-superset)
-[![Get on Slack](https://img.shields.io/badge/slack-join-orange.svg)](https://join.slack.com/t/apache-superset/shared_invite/zt-1jp6hjzrq-H0PlFtToyLWuPiJDuRWCNw)
+[![Get on Slack](https://img.shields.io/badge/slack-join-orange.svg)](http://bit.ly/join-superset-slack)
 [![Documentation](https://img.shields.io/badge/docs-apache.org-blue.svg)](https://superset.apache.org)
 
 <img
@@ -129,7 +129,7 @@ Want to add support for your datastore or data engine? Read more [here](https://
 ## Get Involved
 
 - Ask and answer questions on [StackOverflow](https://stackoverflow.com/questions/tagged/apache-superset) using the **apache-superset** tag
-- [Join our community's Slack](https://join.slack.com/t/apache-superset/shared_invite/zt-1jp6hjzrq-H0PlFtToyLWuPiJDuRWCNw)
+- [Join our community's Slack](http://bit.ly/join-superset-slack)
   and please read our [Slack Community Guidelines](https://github.com/apache/superset/blob/master/CODE_OF_CONDUCT.md#slack-community-guidelines)
 - [Join our dev@superset.apache.org Mailing list](https://lists.apache.org/list.html?dev@superset.apache.org)