Updated MAINTAINERS.md file for Tier 2 and Tier 3

[natalialuzuriaga]

Updated MAINTAINERS.md file for Tier 2 and Tier 3

Problem

Currently, there is no MAINTAINERS.md file for Tier 2. The current Tier 3 MAINTAINERS.md is actually the Tier 2 version. Additionally, the Tier 3 MAINTAINERS.md is missing a table with information on member roles and responsibilities.

Solution

• Added Tier 2 MAINTAINERS.md
• Updated Tier 3 MAINTAINERS.md, taken from: https://github.com/DSACMS/dedupliFHIR/blob/main/MAINTAINERS.md?plain=1
• Added member roles and responsibilities table to Tier 3.

[natalialuzuriaga]

@decause-gov Along with reviewing the changes above, please let me know if you want any edits for the Tier 4 MAINTAINERS.md: https://github.com/DSACMS/repo-scaffolder/blob/main/tier4/%7B%7Bcookiecutter.project_slug%7D%7D/MAINTAINERS.md