Code refactoring: breaking changes in page schemas

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It is needed to update schemas due to the changes in the backend.

Change in the backend:Women-Coding-Community/wcc-backend#289

Update page schemas:

• In FeedbackItem schema: boolean mentee is replaced with MemberType memberType.
  memberType is mandatory field (not null). (please see screenshot below)

• FeedbackSection added to LandingPage

Additional info: All memberTypes fields in json files are capitalized. For example, COLLABORATOR/collaborator is now diplayed (serialized in json files) as Collaborator.

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@dricazenck @stepsen89 These changes are not deployed to the fly server yet - @dricazenck please share with us if you have some time frame when you plan to upload the changes. Thank you!