[DOC] Make it clear what happens when brokerCertChainAndKey certificate is updated

[scholzj]

Type of change

• Documentation

Description

When using the brokerCertChainAndKey option to configure a custom listener certificate, the operator will automatically detect changes and roll the brokers when it is updated. This is not clear from the docs, but it should be so that:

• Users know to expect a rolling update when they change it (and e.g. not update the secret in the peak time of their business day)
• Users know that they should not need to do anything more after updating the secret -> especially important when integrating with other tooling and certificate providers with shorter lifespans such as Let's Encrypt.

Checklist

• Update documentation