indexer: support per-parameter apply_method on aws_db_parameter_group

[UnbornAztecKing]

Adds the workspace-level knobs needed to describe a real indexer/ deployment without forcing destructive replacements when imported live state diverges from the previously hard-coded module.

variable	type	default	controls
rds_parameter_group_parameters	map(object({ value, apply_method = optional("immediate") }))	prior 19-entry value-only map, re-shaped	parameters on aws_db_parameter_group.main; static params (e.g. rds.logical_replication) can now declare apply_method = "pending-reboot" and not trigger cannot_update replace
rds_main_copy_tags_to_snapshot	bool	true	aws_db_instance.main.copy_tags_to_snapshot
ecs_container_insights	string (enhanced/enabled)	enhanced	containerInsights on aws_ecs_cluster.main in indexer/ and on each module.validator invocation (full_node, snapshot, backup) via new module var container_insights
msk_open_monitoring_jmx_exporter_enabled	bool	true	aws_msk_cluster.main.open_monitoring.prometheus.jmx_exporter.enabled_in_broker
msk_open_monitoring_node_exporter_enabled	bool	true	…node_exporter.enabled_in_broker

Driver

Adopting the live testnet PG into TF state (testnet-indexer-apne1-db-parameter-group-postgres-17) surfaced rds.logical_replication with apply_method = pending-reboot. The prior map(string) schema could not encode apply_method, producing an unresolvable cannot_update diff that planned a full PG replace. Same story for the other four knobs: live testnet diverges from the hard-coded value, no var existed to declare the live value.

Backward compatibility

• Workspaces using the default for rds_parameter_group_parameters are unaffected.
• Workspaces that overrode it (testnet) must migrate to the new object shape — { value = "..." }, optionally { value = "...", apply_method = "pending-reboot" }.
• All other new vars have defaults equal to the prior hard-coded literal.

Reviewer brief

• indexer/variables.tf — the five new variables.
• indexer/rds.tf — dynamic "parameter" now consumes the object map.
• indexer/ecs.tf, indexer/msk.tf — single-line literal → var substitution.
• modules/validator/{ecs,variables}.tf — module-level container_insights var, propagated by indexer's three module.validator callers.

Out of scope

• Importing externally-named parameter groups in mainnet/internal/staging workspaces.
• Aligning var.rds_parameter_group_name (instance attachment) with aws_db_parameter_group.main.name.