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[bot]]

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 :warning:
client/pyroclient/client.py	75.00%	1 Missing :warning:
src/app/api/api_v1/endpoints/cameras.py	90.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ 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](https://app.codecov.io/gh/pyronear/pyro-api/pull/371/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pyronear) | Coverage Δ | | |---|---|---| | [backend](https://app.codecov.io/gh/pyronear/pyro-api/pull/371/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pyronear) | `85.99% <91.48%> (+0.19%)` | :arrow_up: | | [client](https://app.codecov.io/gh/pyronear/pyro-api/pull/371/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pyronear) | `92.06% <75.00%> (+0.26%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pyronear#carryforward-flags-in-the-pull-request-comment) to find out more.

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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?