Add significant performance improvements for composer v2

[xvilo]

Currently, Repman is quite slow on the /packages.json endpoint, this due it's requesting all JSON files for every package from S3. From composer 2.0 and onwards, the API has been changed, it does not need to have all packages available any more. But, it now may provide the providers-url and metadata-url. This is where information for a specific package can be found. Thus, it does not have to wait for all packages to be resolved AND it's able to request info about the needed packages only.

If people are still using composer 1.0 it will add back the old data, so performance impact will only be solved for people using v2. It will however, show an extra warning.

Curl request statistics for /packages.json repo endpoint:

Currently:

{
"time_redirect": 0.000000,
"time_namelookup": 0.193779,
"time_connect": 0.203508,
"time_appconnect": 0.229232,
"time_pretransfer": 0.230318,
"time_starttransfer": 19.032120,
"time_total": 23.855557,
"size_request": 107,
"size_upload": 0,
"size_download": 1269753,
"size_header": 352
}

with these changes:

{
"time_redirect": 0.000000,
"time_namelookup": 0.018870,
"time_connect": 0.022539,
"time_appconnect": 0.042854,
"time_pretransfer": 0.043032,
"time_starttransfer": 0.260770,
"time_total": 0.260906,
"size_request": 177,
"size_upload": 0,
"size_download": 3345,
"size_header": 352
}

Looking at the total request time for our internal production deployment, we're going from a request time of 24 seconds, to around 260 milliseconds.

[codecov[bot]]

Codecov Report

Merging #608 (180897b) into master (f82251f) will decrease coverage by 0.01%. The diff coverage is 96.96%.

@@             Coverage Diff              @@
##             master     #608      +/-   ##
============================================
- Coverage     99.16%   99.14%   -0.02%     
- Complexity     1910     1917       +7     
============================================
  Files           301      303       +2     
  Lines          6072     6092      +20     
============================================
+ Hits           6021     6040      +19     
- Misses           51       52       +1     

Impacted Files	Coverage Δ
src/Controller/RepoController.php	98.70% <95.00%> (-1.30%)	:arrow_down:
src/Service/Composer/ComposerEnvironment.php	100.00% <100.00%> (ø)
...rc/Service/Composer/ComposerEnvironmentFactory.php	100.00% <100.00%> (ø)

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[xvilo]

Possible todo: add test for composer v1 and V2 package endpoint differences. Also test this with an invalid user agent. This will fix the missing coverage

[akondas]

I'm willing to accept this ... but can you add more tests for that? I'm not sure if i'm follow (sorry) and tests will give me more confidence :wink: