Tenant configuration is modified even if file saving fails

[koivunej]

Noted by @problame in #3446 (comment)

Relevant code:

neon/pageserver/src/tenant/mgr.rs

Lines 288 to 300 in 0ec84e2

	pub async fn update_tenant_config(
	conf: &'static PageServerConf,
	tenant_conf: TenantConfOpt,
	tenant_id: TenantId,
	) -> anyhow::Result<()> {
	info!("configuring tenant {tenant_id}");
	let tenant = get_tenant(tenant_id, true).await?;
	tenant.update_tenant_config(tenant_conf);
	let tenant_config_path = conf.tenant_config_path(tenant_id);
	Tenant::persist_tenant_config(&tenant.tenant_id(), &tenant_config_path, tenant_conf, false)?;
	Ok(())
	}

[koivunej]

This did have the added benefit that we were able to modify some pitr_cutoffs recently on disk full situation.