show message on courses index for users with no enrollments
show message on courses index for users with no enrollments

test plan:
* enable course catalog feature on the root account
* as an account admin not enrolled in any courses,
 the courses index should have a link to "Browse More Courses"
 and a message explaining that you have no enrollments

closes #CNVS-30180

Change-Id: I1b062d4c76a3b6741057d7983c5cfddf678b368c
Reviewed-on: https://gerrit.instructure.com/84142
Tested-by: Jenkins
Reviewed-by: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>
QA-Review: Deepeeca Soundarrajan <5bcd4b623f00b7fc2942cd1c65c245b30a48a61f@instructure.com>
Product-Review: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

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