feat(markdown): make <br> consistent with line breaks

With the `` component:

## Question

- when adding a single line break in between text, does it add 0 or 1 `
` in the rendered html?
- when adding double line breaks, does it add 1 or 2 `
` in the rendered html?

**IF:**
- adding a single line break == 1 `
` in the rendered html
- adding double line breaks == 2 `
` in the rendered html

**THEN:** This ticket can be closed (but I believe it doesn't)

## Goal

**IF:**
- adding a single line break == 0 `
` in the rendered html
- adding double line breaks == 1 `
` in the rendered html

**THEN:** I want to change it to
- adding a single line break == 1 `
` in the rendered html
- adding double line breaks == 2 `
` in the rendered html