[ECO-2188] Revise indexer NAT gateway(s), rules, autoscaling

[alnoki]

Description

cfn-lint

The following cfn-lint issues have been addressed, enabling template rules:

1. [Bug] Impossible, rules-unaware condition errors aws-cloudformation/cfn-lint#3630
2. [Bug] Rules support Condition, which is not a rule-specific intrinsic function aws-cloudformation/cfn-lint#3710

Hence:

1. Bump cfn-lint version in pre-commit config.
2. Convert cascaded MaybeDeploy* conditions to Deploy* rules with asserts.

NAT gateways

1. Update NAT gateway architecture to have redundant NAT gateways per AWS best
   practices.
2. Create new private route tables and subnet associations for one NAT gateway
   per subnet.
3. Abstract associated resource creation using Fn::ForEach operator.

Autoscaling

1. Abstract autoscaling targets and policies for broker and PostgREST.
2. Use target autoscaling for scaling out, and custom step scaling for scaling
   in, effectively silencing an erroneous alarm for low CPU usage on an idle
   single container.

Miscellaneous

1. Update README line breaking and stack name setting commands.
2. Update README to reflect new simplified Deploy* parameters.
3. Document autoscaling and NAT gateway architectures.
4. Remove extraneous !Ref and/or !Sub commands where not needed.
5. Bump processor and broker binaries per recent code changes.
6. Remove general cache against /* due to wildcard issues.

Testing

REST and WS public endpoints were verified before the binaries were updated in 74c71ee, which required a redeployment of the stack due to breaking migrations reversions. Once backfilled, the endpoints can be tested again.

Checklist

• Did you update relevant documentation?
• Did you check all checkboxes from the linked Linear task?