Allow inserting the changelog inside a file using a marker

[jooola]

I propose to add a way to insert the generated change log in an existing file at a marker in this file.

For example I want to keep a header on the top of the change log file, and I don't want to regenerate the whole change log every time. I generate the change log for every release so I can fix outdated information and typos, and they should not be regenerated.

# Changelog title

This is part of the file header, it should stay at the top of the file.

<!-- git-chlog insert-marker -->

## 3.0.2 Some release entry (2023-02-21)

- My commit description

After running git-chlog, e.g git-chlog 3.0.2..3.1.0 --insert-into CHANGELOG.md

# Changelog title

This is part of the file header, it should stay at the top of the file.

<!-- git-chlog insert-marker -->

## 3.1.0 Some release entry (2023-03-21)

- My commit description

## 3.0.2 Some release entry (2023-02-21)

- My commit description

Expected Behavior

Insert the generated change log inside a file using a marker

Actual Behavior

This feature does not exists.

Your Environment

• git-chglog version: git-chglog version 0.15.3