[spiral/monolog-bridge] Adding the ability to configure the Monolog messages format

[msmakouz]

Q	A
Bugfix?	❌
Breaks BC?	❌
New feature?	✔️
Issues	#989

What was changed

Added the ability to configure the Monolog messages format via environment variable MONOLOG_FORMAT.
We can't add the format parameter to the configuration file because it is needed in the logRotate method, which is used to add handlers to the configuration file:
https://github.com/spiral/app/blob/master/app/src/Application/Bootloader/LoggingBootloader.php#L20

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.28% ⚠️

Comparison is base (cc53ed1) 83.95% compared to head (0651d8b) 83.67%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #994      +/-   ##
============================================
- Coverage     83.95%   83.67%   -0.28%     
- Complexity     6087     6093       +6     
============================================
  Files           800      801       +1     
  Lines         17141    17197      +56     
============================================
- Hits          14390    14389       -1     
- Misses         2751     2808      +57     

Files Changed	Coverage Δ
...ridge/Monolog/src/Bootloader/MonologBootloader.php	0.00% <0.00%> (ø)
.../Bridge/Monolog/tests/Config/MonologConfigTest.php	0.00% <0.00%> (ø)
src/Bridge/Monolog/tests/RotateHandlerTest.php	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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