cz ch <tag> prints the whole changelog if tag_format is not set #622

Description

Removing the tag_format config from the pyproject.toml results in commitizen not being able to read the changelog for specific tags (it always prints the whole changelog). If tag_format is a required parameter it should be noted in the documentation. Otherwise tag_format should default to $version, since this is how it is initialized.

This can cause a lot of confusion for existing projects that are introducing commitizen in their workflows without using cz init and didn't add tag_format explicitly in the pyproject.toml.

Steps to reproduce

Give the following example setup

git init
cz init
git add . && git commit -m "feat: add pyproject"
cz bump
touch file1 && git add file1 && git commit -m "feat: add file1"
cz bump

Now check the changelog of the latest version

cz ch 0.2.0
cat CHANGELOG.md
## 0.2.0 (2022-11-27)

### Feat

- add file1

Remove tag_format line from pyproject.toml

Check again

Current behavior

cz ch 0.2.0
cat CHANGELOG.md
## 0.2.0 (2022-11-27)

### Feat

- add file1

## 0.1.0 (2022-11-27)

### Feat

- add pyproject

Desired behavior

cz ch 0.2.0
cat CHANGELOG.md
## 0.2.0 (2022-11-27)

### Feat

- add file1

Screenshots

No response

Environment

cz version: 2.37.0
python version: 3.10.8