front: stdcm: identify fake service tracks and report takeover stops

[eckter]

See https://github.com/osrd-project/osrd-confidential/issues/946 https://github.com/osrd-project/osrd-dags/issues/675

We add fake service track as a temporary solution to get takeover stops.

We need to identify when the train enters and leave this fake track (using fake operational points). We'd then remove the fake OPs and replace them with an extra stop.

EDIT: as the output table is exclusively built from the front-end, this is actually a front issue

The back-end would return data that would render like this:

OP	CH	end	passage	start
=	BV		02:45
=	P2		02:45
=	RL		02:45
=	TR		02:45
OVERTAKE_0_A;Ambérieu	0		02:45
OVERTAKE_1_B;Ambérieu	0		03:08
Ambérieu	P3		03:08
=	FR		03:09
=	FR		03:09

We need it to look like that, like a single stop:

OP	CH	end	passage	start
=	BV		02:45
=	P2		02:45
=	RL		02:45
=	TR		02:45
Ambérieu	0	02:45	(23 min)	03:08
Ambérieu	P3		03:08
=	FR		03:09
=	FR		03:09

We can discuss the formatting of the initial OP field further, it's not set in stone. The way I imagine it would be to match any consecutive OVERTAKE.*, and then only use what's after a ;.

Note: this is all a temporary solution, it would be best to have a lightweight commit that can be git reverted.