DEVX-5663 Add SIP observeForceMute flag

[superchilled]

This PR provides clarity around use of the observe_force_mute option when making a SIP call using the Sip#dial method.

Description

Including '"observeForceMute":"true" as part of the JSON payload for call to the /dial API endpoint indicates whether the SIP end point observes force mute moderation. This property can be included in the payload by adding it as an option in the opts hash passed to Sip#dial method. No changes were required to the implementation of the method, since the method can already accept observe_force_mute as a key in the opts hash (the method is very lenient with regards to keys that can be included in the hash).

The only changes were to the code comments in the Sip#dial method definition, and to the relevant specs.

Motivation and Context

Ongoing development to roll out new API features.

How Has This Been Tested?

Existing spec has been updated to include the option for observe_force_mute. Test suite has been run to pass.

Example Output or Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Note: not technically a bug-fix, but not technically implementing a new feature either, but clarifies/ highlights the ability to use a new feature.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• [] I have added tests to cover my changes.
• All new and existing tests passed.

[superchilled]

@pardel I think this one is ready to merge now.