Charge as a regular action
You found what there is to find: "Charge" is not a regular action you can take.
The common conception seems to be that a player character is not big enough to charge something efficiently. In fact, most (to not say all - I couldn't find any that wasn't at least Large, but I don't like saying "all") of the beasts with the Charge feature are large beasts, while player characters are only medium. Example of Charge feature from the Elk:
Charge. If the Elk moves at least 20 feet straight towards a
target and then hits it with a ram attack on the same turn, the
target takes an extra 7 (2d6) damage. If the target is a creature,
it must succeed on a DC 13 Strength saving throw or be
knocked prone.
The Cavalier - Ferocious Charger
Additional to the Charger feat, the Cavalier subclass of Fighter, described in Xanathar's Guide to Everything, p. 30 and 31, has the Ferocious Charger feature:
Starting at 15th level, you can run down your foes,
whether you’re mounted or not. If you move at least 10
feet in a straight line right before attacking a creature
and you hit it with the attack, that target must succeed
on a Strength saving throw (DC 8 + your proficiency bonus + your Strength modifier) or be knocked prone. You
can use this feature only once on each of your turns.
This is probably the closest you can get to the Charge feature from beasts, although it does not add extra damage and only comes by 15th level, so you might be disappointed.
So, TL;DR: Charge is a special feature from a specific class, or you could take the Charger feat, but it is not a regular action anyone could take.
The Move + Shove scenario
As a side note, I would like to address this statement:
In other words, the player's running momentum is completely decoupled from the shove and gives them no advantage.
Page 173 from the PHB describes advantage and disadvantage in detail. In particular
The DM can also decide that circumstances
influence a roll in one direction or the other and grant
advantage or impose disadvantage as a result.
So, for example, if the DM finds that a Half-orc moving-and-shoving (similar to Charging) into a Gnome (which is small) should give the half-orc some advantage, ruling that the Athletics Check is made with advantage for the half-orc (or disadvantage for the gnome, since it is a contest) is not even a house-rule, it's just a ruling based on the book's RAW.
I.e., you don't need a written rule to grant advantage or disadvantage, the rules already cover the fact that the DM can grant them based on circumstances they find relevant.
Best Answer
No, because the mount acts on a separate turn from yours
Charger says:
Step 1
So the basic idea of your step 1 is perfectly fine. You take the dash action, which is allowed and this means that your movement increases. However, do note that this doesn't affect your mount at all (so no "increasing speed by 10 ft" for example). Also it is good to note here that dash does not modify any speed at all; it simply grants additional movement.
Step 2
The problems start around step 2 however.
Since you have used the dash action, you may now take a bonus action attack against any enemy in range. However, in order to get the +5 bonus damage as well you must first move at least 10 feet in a straight line immediately before taking this bonus attack.
You might think that moving your mount would work, but it does not. This is because a controlled mount seems according to the rules to act on a turn separate from yours. Per Jeremy Crawford:
Thus, you cannot intersperse your and its movement and actions (see this answer for more details on this and the debate surrounding it).
This means that you must end your turn in order to have the mount move towards the opponent. Since it is no longer your turn, you cannot take the bonus attack (bonus actions must be taken on your turn) or the +5 damage (because it is no longer immediately after your dash action).
However, if you dashed then dismounted and moved 10+ feet in a straight line towards an enemy you would definitely be able to get your bonus attack with +5 damage.