Enhance: Limit the rate of responses to API calls to a node and add metrics for incoming API calls

[capt4ce]

Description

The current implementation does not have rate limiter in for API request coming to a node. This causes a problem to explorer nodes in alpha. The 2 explorer were stuck because of (suspected) being overwhelmed by explorer Backend software's API request to the nodes.

Because of this, it arises the need for having metrics monitoring set up for incoming API calls

Breakdown

• add monitoring metrics for API calls
• Apply rate limiting mechanism to the nodes

Expected behavior

The rate of API calls responded by a node should be controlled.