[GS] Improve the display logic for the default state of navigational search

[ryankeairns]

Related to #75040

While the critically of this issue is low until we have additional providers, the 'display apps only when the term is empty' logic that is in the search bar should be cleaned up. It's also worth noting that this is dependent upon #75040 , wherein we'll determine whether or not to change the default state design altogether, possibly moving away from the initial app list.

Ideally, we would just not be performing a GS search and, instead, retrieving the full app list from core's application.applications$ API. That would avoid unnecessary calls to the backend, and avoid having to increase the max result constant to a value that is too high for other providers. Also, the GS API should just not perform any call to the providers when the term is empty.

Originally posted by @pgayvallet in #78741 (comment)

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[elasticmachine]

Pinging @elastic/appex-sharedux (Team:SharedUX)