feat: Added new flags to support release notes header and footer.

[jnovikov]

Created two flags for release generation.
--release-footer
--release-header
These flags can help you to add custom changelog text before/after changes that are generated by git log.

This commit is based on this issue:
#1131

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@4719763). Click here to learn what that means.
The diff coverage is 63.88%.

@@            Coverage Diff            @@
##             master    #1212   +/-   ##
=========================================
  Coverage          ?   83.66%           
=========================================
  Files             ?       58           
  Lines             ?     3311           
  Branches          ?        0           
=========================================
  Hits              ?     2770           
  Misses            ?      460           
  Partials          ?       81

Impacted Files	Coverage Δ
pkg/context/context.go	100% <ø> (ø)
internal/pipe/changelog/changelog.go	98.27% <100%> (ø)
main.go	48.85% <13.33%> (ø)

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[caarlos0]

I'll take a look at some point, sorry for the delay so far

[caarlos0]

overall looks good, just a few comments there :)

[caarlos0]

Thanks @jnovikov and so sorry for the delay 🙏

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.