* 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
* 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
* allow ordering using columns from object relationships, close#463
* validate table fields in nested insert
* add tests
* add docs
* change 'table_order_by' type from enums to ordered map
* remove unwanted code from 'Schema.hs' file
* 'AnnGObject' is not list of field name and value tuple
* update docs for new order_by type
* use 'InsOrdHashMap' for 'AnnGObj'
* handle empty fields in order_by
* remove '_' prefixes for asc/desc
* fix the changed order_by syntax across the repo
* support for count and aggregations on columns, close#786
* support explain query for aggregations
* '<arr-rel>_agg' in '<table>' type, fix order by for aggregations
* add 'allow_aggregations' key in select permissions
* Add checkbox to toggle count and aggregations on columns on select permission
* align aggregation checkbox with columns div
* improve readability of the generated sql
* alias is needed at the top level aggregation
* throw internal errors for unexpected fields
* rename SelFld to more readable TableAggFld
* rename agg to aggregate
