fix(lint): export types that are being returned by some methods

[nikoksr]

Description

The revive linter complained about certain types that were not exported but being used as return values by certain methods. I exported these types now and added the missing comments for them.

Motivation and Context

GitHub pipeline was stuck due to the linter complaining about this issue.

How Has This Been Tested?

Ran the linter and test suit locally.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (no code change)
• Refactor (refactoring production code)
• Other

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

Base: 55.91% // Head: 55.91% // No change to project coverage 👍

Coverage data is based on head (df3fb4c) compared to base (e1df177).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #374   +/-   ##
=======================================
  Coverage   55.91%   55.91%           
=======================================
  Files          21       21           
  Lines         719      719           
=======================================
  Hits          402      402           
  Misses        286      286           
  Partials       31       31           

Impacted Files	Coverage Δ
service/lark/common.go	100.00% <100.00%> (ø)
service/lark/custom_app.go	53.44% <100.00%> (ø)
service/lark/webhook.go	39.13% <100.00%> (ø)

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[nikoksr]

@svaloumas fyi, I just noticed that the PR pipeline is stuck. Found it kinda weird that there are seven open PRs.

On further inspection it appeared that the auto-merge didn't get green light due to the linter failing. Explanation is up above. Not too sure how this didn't happen earlier tbh. Anyways, this should fix it. Just wanted to quickly update you on this, too.