Add a complementary `createSecret()` API - with container URL method

[lbroudoux]

Reason/Context

This is required by microcks/microcks-quarkus#164

As of today, you can just declare sects to be created using the withSecret() method before the container is started. However, in the case of Quarkus DevServices, the container is started before secrets can actually be created. Also, we'd probably need to allow unit/integration tests to create additional secrets and because they cannot have access to the container instance, we need to do this by overriding the container URL

Description

Provide:

• a public createSecret(secret) method on the MicrocksContainer class
• a public static createSecret(microcksContainerURL, secret) method on the MicrocksContainer class

Implementation ideas

The existing withSecret() method will be refactored to use the public createSecret() one.