Merge definitions of shared functions from slack-message-sender and rotate-signify-certificate

[KacperMalachowski]

Description

With current repository structure we cannot easily share python code between our cloud runs slack-message-sender and rotate-signify-certificate, because directory structre uses - in the names.

The proposed solution is to remove dashes from directory name, which will be also consistent with pkg directory structure.

Acceptance Criteria

• Remove dashes from directories names
• Create common file for get_pubsub_message, preapre_log_fields, prepare_success_response, LogEntry and prepare_error_response python functions and class.
• Update slack-message-sender and rotate-signify-certificate to use common version of those functions