Added lint rule for checking exported methods

[cpheps]

Description of Changes

Setup the linter to enforce comments on exported methods.

Please check that the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• Add a changelog entry (for non-trivial bug fixes / features)
• CI passes

[codecov]

Codecov Report

Merging #571 (ce3d00b) into master (3b23e5c) will decrease coverage by 1.94%.
The diff coverage is 68.29%.

@@            Coverage Diff             @@
##           master     #571      +/-   ##
==========================================
- Coverage   76.69%   74.74%   -1.94%     
==========================================
  Files         132      132              
  Lines        8308     9993    +1685     
==========================================
+ Hits         6371     7469    +1098     
- Misses       1473     2061     +588     
+ Partials      464      463       -1     

Impacted Files	Coverage Δ
operator/buffer/buffer.go	75.86% <ø> (-1.92%)	⬇️
operator/buffer/memory.go	71.60% <ø> (-3.74%)	⬇️
...builtin/input/aws/cloudwatch/cloudwatch_persist.go	75.00% <ø> (-6.82%)	⬇️
operator/builtin/input/azure/event_hub.go	0.00% <0.00%> (ø)
operator/builtin/input/azure/event_hub_config.go	90.91% <ø> (-1.09%)	⬇️
operator/builtin/input/file/finder.go	100.00% <ø> (ø)
operator/builtin/input/file/reader.go	53.05% <0.00%> (-5.73%)	⬇️
operator/builtin/input/http/config.go	97.56% <ø> (-0.29%)	⬇️
operator/builtin/input/journald/journald.go	58.76% <ø> (-1.83%)	⬇️
operator/builtin/input/udp/udp.go	73.49% <ø> (-1.51%)	⬇️
... and 156 more

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