es_out: support Upstream Servers with configuration overriding

[mabrarov]

Implementation of Upstream feature for the Elasticsearch output plugin.

Refer to fluent/fluent-bit#7608 for the changes in Fluent Bit code.

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[mabrarov]

This pull request is waiting for review of fluent/fluent-bit#7608

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[cnorris-cs]

I left suggestions, but I've added my technical writing-based approval based on that to keep this moving.

Primarily, I was looking to help the table be more consistent and readable, while implementing some style-based suggestions for consistency.

[mabrarov]

Hi @cnorris-cs,

I applied some (!) parts of your suggestions as well as introduced additional changes for consistency with your suggestions. Please take a look at this pull request one more time when you have time. Some of the changes are implemented in dedicated commits (for ease of revert in case of concerns) - please let me know if I need to squash all commits into a single one.

Thank you for your review.

[lockewritesdocs]

@fluent/fluent-bit-maintainers -- this PR needs a technical review.

[esmerel]

This still looks ok to me from a writing perspective.

[esmerel]

Couple of minor stylistic suggestions for consistency, but these docs changes look good to me otherwise.

[esmerel]

Suggested change

	| `Host` | IP address or hostname of the target Elasticsearch instance. | `127.0.0.1` | Yes. Default value isn't applicable for NODE section of Upstream configuration, which **requires** Host to be specified. |
	| `Port` | TCP port of the target Elasticsearch instance. | `9200` | Yes. Default value isn't applicable for NODE section of Upstream configuration, which **requires** Port to be specified. |
	| `Host` | IP address or hostname of the target Elasticsearch instance. | `127.0.0.1` | Yes. Default value isn't applicable for NODE section of Upstream configuration, which requires `Host` to be specified. |
	| `Port` | TCP port of the target Elasticsearch instance. | `9200` | Yes. Default value isn't applicable for NODE section of Upstream configuration, which requires `Port` to be specified. |

We don't use bold for emphasis, per our style guide. Also ensuring keys are code fenced.

[mabrarov]

Applied suggested changes. Thank you.

[esmerel]

Suggested change

	The `http_proxy`, `no_proxy`, and `TLS` parameters used for AWS Sigv4 Authentication
	(for connection of plugin to AWS to generate authentication signature) are never
	picked from the `NODE` section of the
	[Upstream](../../administration/configuring-fluent-bit/classic-mode/upstream-servers.md)
	configuration. However, `TLS` parameters for connection of the plugin to
	Elasticsearch **can** be overridden in the `NODE` section of Upstream, even if AWS
	authentication is used.
	The `http_proxy`, `no_proxy`, and `TLS` parameters used for AWS Sigv4 Authentication (for connection of plugin to AWS to generate authentication signature) are never picked from the `NODE` section of the [Upstream](../../administration/configuring-fluent-bit/classic-mode/upstream-servers.md) configuration. However, `TLS` parameters for connection of the plugin to Elasticsearch can be overridden in the `NODE` section of Upstream, even if AWS authentication is used.

Unfortunately, GitBook messes up the rendering of properly linewrapped text :(

[mabrarov]

Applied suggested changes. Thank you.