Config flag for enabling/disabling preferences

[steve-chavez]

Problem

Certain Prefer options need to be disabled in some cases, see #2777.

We also have a special config for Prefer: tx=commit, see db-tx-end.

Ideally we wouldn't need a special config for each case.

Proposal

Have a single config that enables or disables all preferences:

-- by default all preferences are enabled, so empty
server-preferences-disabled = ""

-- disable count: exact
server-preferences-disabled = "count=exact"

-- disable timezone
server-preferences-disabled = "timezone"

Notes

• Maybe we can deprecate db-tx-end after this. cc @wolfgangwalther

[wolfgangwalther]

Maybe we can deprecate db-tx-end after this.

This setting does not translate 1:1 to the preferences-disabled, because it also set's a default value.

I'm undecided whether I find a shared preferences-disabled config a good or bad idea.