Enable sidecar injection by default for namespaces being enrolled into the mesh

[shashankram]

Please describe the Improvement and/or Feature Request
Currently, when a namespace is added to the mesh using the osm namespace add command, sidecar injection is not enabled by default unless the --enable-sidecar-injection flag is passed. This was done based on the requirement that enabling sidecar injection on a namespace could be destructive for new users.

However, this proves to be a bit counterintuitive because the common use case is to enroll a namespace into the mesh and have it injected with sidecars to participate in the mesh.

Scope (please mark with X where applicable)

• New Functionality [ ]
• Install [ ]
• SMI Traffic Access Policy [ ]
• SMI Traffic Specs Policy [ ]
• SMI Traffic Split Policy [ ]
• Permissive Traffic Policy [ ]
• Ingress [ ]
• Egress [ ]
• Envoy Control Plane [ ]
• CLI Tool [X]
• Metrics [ ]
• Certificate Management [ ]
• Sidecar Injection [ ]
• Logging [ ]
• Debugging [ ]
• Tests [ ]
• CI System [ ]
• Project Release [ ]

Possible use cases

This issue is to propose enabling sidecar injection by default with the osm namespace add command, unless --disable-sidecar-injection flag is passed. There are other ways to prevent a namespace from being injected with sidecars and controlling injection on a per pod basis, that make it more reasonable to have the namespace scoped injection enabled by default with the osm namespace add command.

[shashankram]

Resolved by c5147ae