Add delete endpoint for image

[asuresh-code]

Description

Implements a DELETE endpoint /images/<image_id> that:

• Deletes the image metadata from the database
• Deletes the file object in the object store
• Gracefully deals with a situation when the file object with the given object_key doesn't exist

Testing instructions

• Review code
• Check Actions build
• Review changes to test coverage

Agile board tracking

closes #38

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.59%. Comparing base (1620e19) to head (ce62423).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #72      +/-   ##
===========================================
+ Coverage    98.29%   98.59%   +0.30%     
===========================================
  Files           21       21              
  Lines          410      428      +18     
===========================================
+ Hits           403      422      +19     
+ Misses           7        6       -1     

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[joelvdavies]

A few small comments. will look at the tests afterwards. This PR may have some minor conflicts with the get branch so will probably need merging into to this branch one it is merged.

[joelvdavies]

Minor comments works well.

[joelvdavies]

LGTM