Bring consistency into status condition messages

[pleshakov]

We have some inconsistent messages in status conditions of resources.

(below, we use ConditionType/Status/Reason notation)

A few examples:

• "The route is accepted" for HTTPRoute Accepted/True/Accepted . However, we have "GatewayClass is accepted" for GatewayClass Accepted/True/Accepted.
• "unsupported value" for Listener Accepted/False/UnsupportedValue. Note that in most other messages, first letter is capitalized.
• "invalid backendTLSPolicy" for BackendTLSPolicy Accepted/False/Invalid. Note: first letter is not capitalized, backendTLSPolicy is spelled differently from other similar places. Needed "BackendTLSPolicy"

Acceptance criteria:

• Come up with consistent style
• Capture rules if necessary
• Bring messages with accordance to the style