Model providers should not be displayed in the connectors UI

[nipunayf]

Description

Model providers are client classes and, by default, appear in the connectors page. We have a separate UI to search for model providers, so these should be blacklisted.

Steps to Reproduce

Type ModelProvider in the connectors search UI

Version

1.2.2

Environment Details (with versions)

No response

[KavinduZoysa]

Addressed via ballerina-platform/ballerina-language-server#673