* add types to represent unparsed http gql requests
This will help when we add caching of frequently used ASTs
* query plan caching
* move livequery to execute
* add multiplexed module
* session variable can be customised depending on the context
Previously the value was always "current_setting('hasura.user')"
* get rid of typemap requirement in reusable plan
* subscriptions are multiplexed when possible
* use lazytx for introspection to avoid acquiring a pg connection
* refactor to make execute a completely decoupled module
* don't issue a transaction for a query
* don't use current setting for explained sql
* move postgres related types to a different module
* validate variableValues on postgres before multiplexing subs
* don't user current_setting for queries over ws
* plan_cache is only visible when developer flag is enabled
* introduce 'batch size' when multiplexing subscriptions
* bump stackage to 13.16
* fix schema_stitching test case error code
* store hashes instead of actual responses for subscriptions
* internal api to dump subscriptions state
* remove PlanCache from SchemaCacheRef
* allow live query options to be configured on server startup
* capture metrics for multiplexed subscriptions
* more metrics captured for multiplexed subs
* switch to tvar based hashmap for faster snapshotting
* livequery modules do not expose internal details
* fix typo in live query env vars
* switch to hasura's pg-client-hs
From `alpha-40` we've been using a `WHERE` clause to fetch required rows and generate mutation response. This has a few limitations like the requirement of a primary key/unique constraint. This also returns inconsistent data on `delete` mutation as mentioned in #1794.
Now, we're using `VALUES (..)` (refer [here](https://www.postgresql.org/docs/current/sql-values.html)) expression to form virtual table rows in `SQL` to generate mutation response.
Internal changes:-
- Not to use primary key/unique constraint columns:-
- Revert back to `ConstraintName` from `TableConstraint` in `TableInfo` type
- Remove `tcCols` field in `TableConstraint` type
- Modify `table_info.sql` and `fetchTableMeta` function `SQL`
- A test case to perform `delete` mutation and returning relational objects.
If returning field contains nested selections then mutation is performed in two steps
1. Mutation is performed with returning columns of any primary key and unique constraints
2. returning fields are queried on rows returned by selecting from table by filtering with column values returned in Step 1.
Since mutation takes two courses based on selecting relations in returning field, it is hard to maintain sequence of prepared arguments (PrepArg) generated while resolving returning field. So, we're using txtConverter instead of prepare to resolve mutation fields.
* remove phase one/two distinction and hdbquery typeclass
* move extensions to default-extensions
* switch to LazyTx which only acquires a connection if needed
* move defns from TH module into Ops module
* remove tojson orphan instance for http exception
* remove orphan instance for dmlp1
* getTopLevelNodes will not throw any exceptions
