backward relations should take "@omit many" on foreign table and constraints into account

[ab-pm]

I want to omit some "many" fields on a table (or really, on the whole table).
Unfortunately, the @omit many smart comment only allows me to annotate the table with the foreign key constraint, dropping all its backward relations - instead of having me annotate the referenced table, on which the fields to be dropped are generated. I would enjoy having an omit(foreignTable, "many") check added to the line

graphile-engine/packages/graphile-build-pg/src/plugins/PgBackwardRelationPlugin.js

Line 242 in b6fbfb8

if (shouldAddManyRelation && !omit(table, "many")) {

but I guess that would be a backwards-incompatible change. So if that is not possible, I'd suggest allowing many also on the individual constraints or fields, i.e. at

graphile-engine/packages/graphile-build-pg/src/plugins/PgBackwardRelationPlugin.js

Line 69 in b6fbfb8

if (omit(constraint, "read")) {

graphile-engine/packages/graphile-build-pg/src/plugins/PgBackwardRelationPlugin.js

Line 103 in b6fbfb8

if (keys.some(key => omit(key, "read"))) {

[benjie]

Changing line 69 to if (omit(constraint, "read") || omit(constraint, "many")) with the relevant tests would likely be accepted as a PR 👍

Also apparently we don't have any examples in the docs for many so that'd be welcome too 👍