Feat/backend/add caching and preloading images

[waveyboym]

Description

This pr introduces some caching mechanism for images:

1. Make a request for a low res image
2. A worker in the background will download and cache images thus reducing wait times on request for higher res images
3. Some database functions had a cache attached them especially booking

Fixes # (issue)
#156

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• A handful of unit tests were written in the cache_methods_unit_test.go file

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Attention: Patch coverage is 49.65517% with 73 lines in your changes missing coverage. Please review.

Project coverage is 59.21%. Comparing base (bed657d) to head (3b77179).
Report is 88 commits behind head on develop.

Files	Patch %	Lines
occupi-backend/pkg/database/database.go	29.33%	49 Missing and 4 partials ⚠️
occupi-backend/pkg/cache/cache.go	67.74%	12 Missing and 8 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #244      +/-   ##
===========================================
- Coverage    59.60%   59.21%   -0.40%     
===========================================
  Files            8        9       +1     
  Lines         1634     1758     +124     
===========================================
+ Hits           974     1041      +67     
- Misses         622      672      +50     
- Partials        38       45       +7     

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