feat: set JDBC credentials from environmental variables

[pvannierop]

Problem

At present, database credentials cannot be set via the environment from a container. This method of secret provisioning is widely used on containers running an application. For instance, when database passwords are not yet available when the ConfigMap on Kubernetes that holds the database credentials as database.user and database.password is generated, it is difficult to provide correct database credentials at runtime.

Note: This can be tackled with the valueFromEnv mechanism on Kubernetes.

Solution

This PR adds a small class that acts as JdbcCredentialsProvider that reads JDBC credentials from the CONNECT_JDBC_CONNECTION_USER and CONNECT_JDBC_CONNECTION_PASSWORD environmental variables.

Note: The names were chosen somewhat consistent with official env var nomenclature for connect components described here.

Does this solution apply anywhere else?

• [ ] yes
• [x] no

If yes, where?

Test Strategy

Since this PR adds very little in terms of application logic, I did not add tests for now. When the feature added here is accepted, I would be more that happy to write some tests.

Testing done:

• [ ] Unit tests
• [ ] Integration tests
• [ ] System tests
• [x] Manual tests

Release Plan

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[pvannierop]

I noticed, however, that the expected log messages are not transmitted by this class.