feat: updating authorization flow & added invitation resource Classroom code snippets.

[mahima-desetty]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context.
List any dependencies that are required for this change.

Fixes # (issue)

Is it been tested?

• [x ] Development testing done

Checklist

• [x ] My code follows the style guidelines of this project
• [x ] I have performed a self-review of my own code
• [x ] I have performed a peer-reviewed with team member(s)
• [x ] I have commented my code, particularly in hard-to-understand areas
• [x ] I have made corresponding changes to the documentation
• [x ] My changes generate no new warnings
• [N/A ] Any dependent changes have been merged and published in downstream modules

[snippet-bot]

Here is the summary of changes.

You are about to add 9 region tags.

• classroom/snippets/src/main/java/AcceptInvitation.java:15, tag classroom_accept_invitation
• classroom/snippets/src/main/java/AcceptInvitation.java:56, tag classroom_accept_invitation_code_snippet
• classroom/snippets/src/main/java/CreateInvitation.java:15, tag classroom_create_invitation
• classroom/snippets/src/main/java/CreateInvitation.java:60, tag classroom_create_invitation_code_snippet
• classroom/snippets/src/main/java/DeleteInvitation.java:15, tag classroom_delete_invitation
• classroom/snippets/src/main/java/DeleteInvitation.java:56, tag classroom_delete_invitation_code_snippet
• classroom/snippets/src/main/java/GetInvitation.java:15, tag classroom_get_invitation
• classroom/snippets/src/main/java/GetInvitation.java:56, tag classroom_get_invitation_code_snippet
• classroom/snippets/src/main/java/ListStudentSubmissions.java:138, tag classroom_list_assigned_grades_code_snippet

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