[Performance] Reuse clients for better performance

[alukach]

In #95, we refactored the Source API code to persist the reqwest::Client across requests, taking advantage of connection pooling.

The same logic should be applied when creating clients on our S3 interface code (I currently see 11 instances of client creation):

data.source.coop/src/backends/s3.rs

Line 77 in 6305d65

let client = reqwest::Client::new();

data.source.coop/src/backends/s3.rs

Line 124 in 6305d65

let client = self.create_client()?;

(etc...)

Note that this will be a bit more involved than #95 as the S3Repository and AzureRepository isn't currently persisted across requests in the manner that the SourceApi is. The repositories are created on each call to api_client.get_backend_client():

data.source.coop/src/apis/source/mod.rs

Lines 206 to 242 in 6305d65

	Ok(Box::new(S3Repository {
	account_id: account_id.to_string(),
	repository_id: repository_id.to_string(),
	region,
	bucket,
	base_prefix: prefix,
	auth_method: auth.auth_type,
	access_key_id: auth.access_key_id,
	secret_access_key: auth.secret_access_key,
	}))
	}
	"az" => {
	let account_name: String = data_connection
	.details
	.account_name
	.clone()
	.unwrap_or_default();
	let container_name: String = data_connection
	.details
	.container_name
	.clone()
	.unwrap_or_default();
	let base_prefix: String = data_connection
	.details
	.base_prefix
	.clone()
	.unwrap_or_default();
	Ok(Box::new(AzureRepository {
	account_id: account_id.to_string(),
	repository_id: repository_id.to_string(),
	account_name,
	container_name,
	base_prefix: format!("{}{}", base_prefix, repository_data.prefix),
	}))

While the SourceApi is created just once at application startup:

data.source.coop/src/main.rs

Lines 464 to 468 in 6305d65

	let source_api = web::Data::new(SourceApi::new(
	source_api_url,
	source_api_key,
	source_api_proxy_url,
	));