Graylog output plugin: add connection TTL option

## Feature Request

Add connection TTL option to avoid node overload when using multiple load-balanced GL servers. Request per [comment](https://github.com/influxdata/telegraf/pull/9644#issuecomment-998264644) in PR #9644.

Generic problem description: https://www.ateam-oracle.com/post/long-lived-tcp-connections-and-load-balancers

### Proposal:

Add connection TTL option.

### Current behavior:

Connection are long-lived (keep alive is set by default).

### Desired behavior:

When TTL option is set, connection(s) should be closed and re-established after specified duration elapsed.

### Use case:

Proper load distribution among multiple load-balanced GL servers.

Start by locating the Graylog output plugin and its current long-lived connection or keep-alive setup. Confirm how connection creation and reuse work, then define done as closing and re-establishing connections after the configured TTL while preserving load distribution across multiple Graylog servers.

Written by the indexing model from the issue text.