feat(ampsync): add configurable index creation on table setup

[matiasedgeandnode]

Summary

• Adds --config / AMPSYNC_CONFIG option to specify a TOML file with index definitions
• Indexes are created alongside the table on first startup (no-op if table exists)
• Supports btree/hash/gin/gist/brin methods, unique indexes, column sort order (ASC/DESC), covering indexes (INCLUDE), and partial indexes (WHERE)
• All identifiers validated via sqlparser + pg_escape to prevent SQL injection; WHERE clauses parsed for syntactic validity

Config example

[[index]]
table = "usdc_transfers"
name = "idx_buyer_timestamp"
columns = ["buyer_address", "timestamp desc"]
include = ["value_usdc"]

Test plan

• just check-crate ampsync passes
• just clippy-crate ampsync passes (zero warnings)
• cargo nextest run -p ampsync — unit tests pass (config parsing, SQL generation, validation, identifier rejection)
• Integration: run ampsync with --config ampsync.toml against a fresh DB, verify indexes are created
• Integration: restart ampsync against existing table, verify it skips creation

[tmigone]

I suggest using a different name here, index-config or something like that. Otherwise it sounds like the configuration file to run ampsync, where i would expect to be able to set things like auth, table, etc (basically all other config).