Change default `@context' of devices

[benfrancis]

Currently the default value for the @context of new Thing Descriptions is:

"@context": "https://webthings.io/schemas"

It needs to be changed to:

"@context": [
  "https://www.w3.org/2022/wot/td/v1.1",
  "https://webthings.io/schemas",
]

for W3C compliance.

See also:

• Change @context of Thing Descriptions gateway#2809
• Standardise @context of Thing Descriptions - closes #2809 gateway#3034