Clarify switching TLS configuration with ReplaceServerCertificateAssignment

[HansBusch]

The API cannot update before responding as that potentially breaks the connection.

The specification should clarify this.

[sujithhanwha]

Based on 3/10 meeting, agreed to add a capability to inform the time required for the webserver to update.

[ocampana-videotec]

During the F2F meeting, Hans will fill a PR for adding a new capability.

[sujithhanwha]

Since PR is open for this issue based on 3/13 f2f meeting discussion closing this.