Improve a way db.Session is passed to actions

[bartekn]

The way we pass db.Session to actions is currently broken.

• We do so in multiple places instead of one,
• Because of above it's easy to forgot to prepare a session properly (ex. Clone() it like in services/horizon: Clone DB session for each history endpoint request #2652 or services/horizon: Get historyQ from request, making sure that we use a clone of db.Session. #2743).
• We use context.Context to pass it to actions.

We should talk about a new design (possibly something like in #1861).

[2opremio]

@bartekn do you think this still applies, I recall the actions having a helper for this.