Sort file by reverse lexicographical order before tailing them

[achntrl]

What does this PR do?

Sort file by reverse lexicographiccal order before tailing them. The heuristic is that filenames often contain a datetime information

Motivation

What inspired you to submit this pull request?

Additional Notes

Anything else we should know when reviewing?

[codecov-io]

Codecov Report

Merging #2796 into master will decrease coverage by <.01%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##           master    #2796      +/-   ##
==========================================
- Coverage   57.35%   57.34%   -0.01%     
==========================================
  Files         393      393              
  Lines       25707    25721      +14     
==========================================
+ Hits        14743    14749       +6     
- Misses       9991     9999       +8     
  Partials      973      973

Impacted Files	Coverage Δ
pkg/logs/input/file/file_provider.go	74% <42.85%> (-5.07%)	⬇️

[mnshdw]

Isn't that the same as switching i and j without having to reverse paths before ?

[achntrl]

No because here we sort only filename whereas the reverse ensure the whole filepath is reversed. This covers 2 distinct usecases:

├── abc123
│   ├── 1.log
│   └── 2.log
└── def456
    ├── 1.log
    └── 2.log

where we want the 2.log files to come out first and

├── 2018-01-17
│   └── error.log
└── 2018-01-18
    └── error.log

There are some edge case that are not well handled though, mainly

├── 2018-01-17
│   ├── access.log
│   └── error.log  # <- this one is tailed before 
└── 2018-01-18
    ├── access.log # <- this one
    └── error.log

or

├── abc123
│   ├── 1.log
│   ├── 2.log
│   ├── 3.log  # <-┐
│   ├── 4.log  # <-└ these are not active but tailed before
│   └── 5.log  
└── def456
    ├── 1.log
    └── 2.log  # <- this one which is active in a k8s context

It's hard (impossible?) to find a good solution for this without that is also generic