feat(cameras): add a route to update the last known image of a camera

[frgfm]

This PR introduces the following modifications:

• add a "last_image" column in the Camera table
• every time a camera uses it, it uploads an image, stores it in the bucket (and delete the previous one) + update the DB entry
• update the client & corresponding tests
• update the UML & made it live

Here is the updated UML

(live link: https://dbdiagram.io/d/Pyronear-UML-665a15d0b65d933879357b58)

[codecov]

Codecov Report

Attention: Patch coverage is 90.19608% with 5 lines in your changes missing coverage. Please review.

Project coverage is 86.39%. Comparing base (5ed718e) to head (e9d018a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/app/services/storage.py	87.50%	3 Missing ⚠️
client/pyroclient/client.py	75.00%	1 Missing ⚠️
src/app/api/api_v1/endpoints/cameras.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #371      +/-   ##
==========================================
+ Coverage   86.19%   86.39%   +0.20%     
==========================================
  Files          34       34              
  Lines         920      941      +21     
==========================================
+ Hits          793      813      +20     
- Misses        127      128       +1     

Flag	Coverage Δ
backend	85.99% <91.48%> (+0.19%)	⬆️
client	92.06% <75.00%> (+0.26%)	⬆️

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[frgfm]

Worth noting: @MateoLostanlen we'll have to update the engine. We now have 2 potential high frequency interactions: heartbeat & update image. I suggest reversing the equations to set the adequate frequency (& decorrelate it from the prediction frequency on raspberry pi):

• last image: I'd argue we don't need more often than every 10mins
• heartbeat: this is our way to detect if we have "downtime" on a station. Probably every minute ?

What do you think?