Improve cli for other mephisto commands

[Etesam913]

Just building off of #820

Moves away from the tabulate method in favor of the Table import in rich.

mephisto requesters

mephisto register

Added red color & provided list of valid providers in case the user forgot

mephisto register <provider_name>

mephisto metrics

[codecov-commenter]

Codecov Report

Merging #822 (cabe3c6) into improve-cli-for-mephisto-wut (205bfe1) will decrease coverage by 0.05%.
The diff coverage is n/a.

@@                       Coverage Diff                        @@
##           improve-cli-for-mephisto-wut     #822      +/-   ##
================================================================
- Coverage                         64.66%   64.61%   -0.06%     
================================================================
  Files                               107      107              
  Lines                              9281     9281              
================================================================
- Hits                               6002     5997       -5     
- Misses                             3279     3284       +5     

Impacted Files	Coverage Δ
mephisto/data_model/assignment.py	57.81% <0.00%> (-3.91%)	⬇️
mephisto/data_model/unit.py	78.14% <0.00%> (ø)

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[JackUrb]

LGTM - thanks for these QoL improvements across the codebase!