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

[mesqueeb]

With the <Markdown /> component:

Question

• when adding a single line break in between text, does it add 0 or 1 <br> in the rendered html?
• when adding double line breaks, does it add 1 or 2 <br> in the rendered html?

IF:

• adding a single line break == 1 <br> in the rendered html
• adding double line breaks == 2 <br> in the rendered html

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

Goal

IF:

• adding a single line break == 0 <br> in the rendered html
• adding double line breaks == 1 <br> in the rendered html

THEN: I want to change it to

• adding a single line break == 1 <br> in the rendered html
• adding double line breaks == 2 <br> in the rendered html