Implement Healthcheck status for keys loading

[usmansaleem]

PR Description

• Implement Healthcheck status for keys loading.
• Add AWS endpoint override cli option --aws-endpoint-override (useful for testing against localstack).

Sample healthcheck:

{
	"status": "UP",
	"checks": [
		{
			"id": "default-check",
			"status": "UP"
		},
		{
			"id": "keys-check",
			"status": "UP",
			"checks": [
				{
					"id": "aws-bulk-loading",
					"status": "UP",
					"data": {
						"keys-loaded": 2,
						"error-count": 0
					}
				},
				{
					"id": "config-files-loading",
					"status": "UP",
					"data": {
						"keys-loaded": 0,
						"error-count": 0
					}
				}
			]
		}
	],
	"outcome": "UP"
}

Fixed Issue(s)

#715
#730

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[jframe]

Are these results updated when the keys are reloaded?

[usmansaleem]

correct, these will be re-evaluated during reload.

[jframe]

Can a test be added for the reload case, I think have a test for reloading config so shouldn't be too tricky hopefully 🤞

[jframe]

Also, be good to have a test showing that checks have the appropriate status and error count values

[usmansaleem]

Added it in AWS Secrets Manager AT.

[jframe]

Not sure if this appropriate test or not but would be good to have a test case for config-files-loading check as well

[usmansaleem]

Added healthcheck AT related to config-files-loading.

[jframe]

Can a test be added for the reload case, I think have a test for reloading config so shouldn't be too tricky hopefully 🤞