INDEXER_DB_* environment variables from 2.1.1 are missing from env-vars.md reference

## Problem

The `INDEXER_DB_*` environment variables were introduced in PR #707 (release 2.1.1) and are documented in the [2.1.1 GitHub release notes](https://github.com/cardano-foundation/cardano-rosetta-java/releases#release-2.1.1). They are present in the `.env.docker-compose` and `.env.docker-compose-preprod` templates and referenced by the indexer `application.properties`.

However, they are not listed in `docs/docs/install-and-deploy/env-vars.md`, which is the canonical reference table for environment variables. Only `API_DB_POOL_*` variables (from release 1.2.5) are documented there. The published docs at https://cardano-foundation.github.io/cardano-rosetta-java/docs/install-and-deploy/env-vars confirm this gap.

## Missing entries

All 8 variables should be added with "added in release 2.1.1":

| Variable | `.env.docker-compose` default | `application.properties` default | Overridden by profiles? |
|---|---|---|---|
| `INDEXER_DB_SHOW_SQL` | `false` | `false` | No |
| `INDEXER_DB_MONITOR_PERFORMANCE` | `false` | `false` | No |
| `INDEXER_DB_POOL_MIN_COUNT` | `12` | `5` | Yes (mid=50, advanced=50) |
| `INDEXER_DB_POOL_MAX_COUNT` | `12` | `20` | Yes (mid=50, advanced=150) |
| `INDEXER_DB_POOL_MAX_LIFETIME_MS` | `2000000` | `2000000` | No |
| `INDEXER_DB_POOL_CONNECTION_TIMEOUT_MS` | `100000` | `100000` | No |
| `INDEXER_DB_KEEP_ALIVE_MS` | `60000` | `60000` | No |
| `INDEXER_DB_LEAK_CONNECTIONS_WARNING_MS` | `60000` | `60000` | No |

Note: the `application.properties` inline defaults differ from the `.env.docker-compose` template defaults for `INDEXER_DB_POOL_MIN_COUNT` (5 vs 12) and `INDEXER_DB_POOL_MAX_COUNT` (20 vs 12). The profile files (`.env.docker-compose-profile-entry-level`, `-mid-level`, `-advanced-level`) override only these two pool count variables.

## Suggested fix

Add all 8 variables to the env-vars table in `docs/docs/install-and-deploy/env-vars.md` with the "added in release 2.1.1" column. Note the profile overrides for pool count variables.

Update docs/docs/install-and-deploy/env-vars.md, using the listed .env.docker-compose templates and indexer application.properties to verify the eight INDEXER_DB_* entries. Add the "added in release 2.1.1" information and document the profile overrides and differing pool-count defaults; the canonical table should match the supplied values.

Written by the indexing model from the issue text.