RDS connection modes: Secret & IAM tokens + Password refreshing (#689)

* Sketched database password providers. Support: no password, fixed password, and AWS secret password.
* Drafted IAM token as a database authorization alternative
* Slight reshuffling of db components / modules
* Added password refreshers for MySql and Postgres.
* Simplified initialization of initial connection string
* Reorganized database initialization code a lot.
* Support periodic database password refreshing flow, if configured
* Password refreshers as separate components
* Merge corrections + v0.189.0
* Changelog

CHANGELOG.md

@@ -4,6 +4,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.189.0] - 2024-06-28
+### Added
+- Support multiple methods to access database:
+    - via raw password
+    - via password stored as AWS secret
+    - via generated AWS IAM authentication tokens
+- Support periodic database password rotation with configurable period
+
 ## [0.188.6] - 2024-06-27
 ### Fixed
 - Added missed field to create access token result API