feat: add an access logger for the router

[saltbo]

Description

Which issue(s) this PR fixes:

Fixes #2770

Testing

Checklist:

• I ran tests as well as code linting locally to verify my changes.
• I have done manual verification of my changes, changes working as expected.
• I have added new tests to cover my changes.
• My changes follow contributing guidelines of Fission.
• I have signed all of my commits.

[codecov]

Codecov Report

Merging #2771 (60af3ba) into main (a5f3402) will increase coverage by 0.15%.
The diff coverage is 40.67%.

@@            Coverage Diff             @@
##             main    #2771      +/-   ##
==========================================
+ Coverage   20.87%   21.02%   +0.15%     
==========================================
  Files          68       70       +2     
  Lines        7339     7399      +60     
==========================================
+ Hits         1532     1556      +24     
- Misses       5693     5727      +34     
- Partials      114      116       +2     

Flag	Coverage Δ
unittests	21.02% <40.67%> (+0.15%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/router/httpTriggers.go	0.72% <0.00%> (-0.02%)	⬇️
pkg/router/router.go	0.00% <0.00%> (ø)
pkg/router/accesslog/upstream.go	17.24% <17.24%> (ø)
pkg/router/accesslog/logger.go	86.36% <86.36%> (ø)

... and 1 file with indirect coverage changes

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[shubham-bansal96]

@saltbo I was trying to verify your changes but somehow I am not able to see the logs as mentioned by you in this PR.
I have enabled DISPLAY_ACCESS_LOG env variable in using helm chart and i can see this env variable is being set inside container.
I created a new function and test it, but i can't see the logs for router as you mentioned.

Please let me know if i miss anything in order to get the logs.

[saltbo]

part fixed. it can output the log, but not contains upstream info. @shubham-bansal96

My current implementation is not very feasible. I haven't thought of a better way to get upstream info. If you have any ideas, please let me know.