Optmize NHD High Resolution Querying

[rajadain]

Currently the NHD HR layer uses up a lot of RDS CPU and Read Operations: #3415 (comment)

This can potentially lock up the database for other transactional queries (loading / saving projects, etc), and a single user can bring down the entire system.

This can be especially bad when the users zoom a lot, and can lead to tile requests timing out.

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Find a way to optimize the tile requests to make them faster and lighter. Consider:

• Adding the right index
• Adjusting which stream orders are shown at which level
• Batch generating the tile cache

[rajadain]

This may help https://postgis.net/2014/03/14/tip_intersection_faster/

[rajadain]

The tile cache was batch generated in #3465 (comment)

[rajadain]

This is also a good resource on how to read query plans in general: https://thoughtbot.com/blog/reading-an-explain-analyze-query-plan, such as the one in #3465 (comment)