Use docs-content-team tag in issue templates (Qiskit#3131)

@Qiskit/docs-content-team now exists and tags @beckykd and @abbycross.
Adding to our issue templates.

Author: abbycross

.github/ISSUE_TEMPLATE/courses.yaml

@@ -5,6 +5,7 @@ assignees:
   - jhwatrous
   - livlanes
   - christopherporter1
+  - Qiskit/docs-content-team
 
 body:
   - type: markdown

.github/ISSUE_TEMPLATE/guides.yaml

@@ -2,8 +2,7 @@ name: (GUIDES AND ADDITIONAL RESOURCES 📜) Report a bug/typo or request new co
 description: Report typos, bugs, out-of-date content, broken links, etc. or make a request for new content
 labels: ["content 📄", "needs triage 🤔"]
 assignees:
-  - abbycross
-  - beckykd
+  - Qiskit/docs-content-team
 
 body:
   - type: markdown

.github/ISSUE_TEMPLATE/tutorials.yaml

@@ -4,6 +4,7 @@ labels: ["content 📄", "tutorial 📒", "needs triage 🤔"]
 assignees:
   - miamico
   - nathanearnestnoble
+  - Qiskit/docs-content-team
 
 body:
   - type: markdown

.github/ISSUE_TEMPLATE/ui.yml

@@ -2,8 +2,7 @@ name: UI issue or feature request 📱
 description: Report a rendering or other visual problem with the user interface, or request a new feature.
 labels: ["UI feedback", "infra 🏗️"]
 assignees:
-  - abbycross
-  - beckykd
+  - Qiskit/docs-content-team
   - javabster
   - Eric-Arellano