Fix two remote_timeout configs in ingester_client block

[RangerCD]

What this PR does / why we need it:

1. Expose remote_timeout under pool_config block in yaml config file, as expected in documentation.
2. Fix mismatched flags -ingester.client.healthcheck-timeout and -ingester.client.timeout in documentation.

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

remotetimeout inside pool_config has been renamed to remote_timeout. This change does not affect any previous config file, since remotetimeout has never been actually exposed in yaml before.

loki-local-config.yaml:

ingester_client:
  pool_config:
    remotetimeout: 1s

auth_enabled: false
...

Running with latest version:

> loki -config.file=./loki-local-config.yaml
failed parsing config: ./loki-local-config.yaml: yaml: unmarshal errors:
  line 3: field remotetimeout not found in type distributor.PoolConfig

Checklist

• Documentation added
• Tests updated
• Add an entry in the CHANGELOG.md about the changes.

[kavirajk]

LGTM 👍 Thanks @RangerCD. Now it's more clear :)

[kavirajk]

cc @KMiller-Grafana