add: SMTP client functions with proper timeouts

[badarghal]

What

Adds SMTP protocol client functions with timeouts.

Why

To send mail we need some SMTP client. However default golang implementation lacks timeouts and most libraries are either unable to just check connectivity without sending mail or do not introduce any improvement to what standard golang "net/smtp" library offers. This PR adds functions that wrap standard golang SMTP functions and adds timeouts to connections.

References

• AT-2835
• AT-2246

Checklist

• Tests

[greenbonebot]

Scanning the following files:

pkg/smtp/smtp.go
pkg/smtp/smtp_test.go

Scan: 'pkg/smtp/smtp.go'

Nothing detected in pkg/smtp/smtp.go
Scan took 0.00 seconds

Scan: 'pkg/smtp/smtp_test.go'

Nothing detected in pkg/smtp/smtp_test.go
Scan took 0.00 seconds

[github-actions]

Conventional Commits Report

Type	Number
Added	2

🚀 Conventional commits found.

[codecov]

Codecov Report

❌ Patch coverage is 40.27778% with 43 lines in your changes missing coverage. Please review.
✅ Project coverage is 24.39%. Comparing base (9d27c84) to head (b191dae).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/smtp/smtp.go	40.27%	28 Missing and 15 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #149      +/-   ##
==========================================
+ Coverage   22.43%   24.39%   +1.95%     
==========================================
  Files          27       28       +1     
  Lines         584      656      +72     
==========================================
+ Hits          131      160      +29     
- Misses        441      469      +28     
- Partials       12       27      +15     

Flag	Coverage Δ
postgres-tests	45.11% <ø> (ø)
unit-tests	17.48% <40.27%> (+3.28%)	⬆️

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