Hotfix rsrs static query performance

[tkirschke]

Error

• In dbt Cloud, during an execution of "dbt build" or "dbt docs generate", the Job failed with the error message "This run exceeded your account's run memory limits."
• Occured for Multi Source Entities in incremental runs

Cause of Error

• The background code checks for each source if it was included before, to disable the high-water-mark in such a case for this newly added source
• Here all the rows of each source are loaded into dbt and set as a variable
• With high volumes of data, this variable grows very big and therefore the account's memory is exceeded

Fix

• Instead of selecting all rows for each source, only a COUNT(*) is executed. This works fine, because later on the query results are only used to check if there are any rows, not to actually do something with the data.
• This change is applied for all multi-source entities (Hubs, Links, NH-Links, Rec-Track Satellites), for all databases

[bschlottfeldt]

Everything looks good to me :)