Centralize RPC health monitoring

[aditya1702]

What

• Currently, the code for tracking RPC health is duplicated across both the ingest server and the api server (when creating the channel accounts). This PR organises the RPC heartbeat tracking in a central location and simplifies its design.
• Updated tests accordingly.

Why

The current solution for tracking rpc health was not a simple one and had some code duplication which are resolved in this PR.

Known limitations

NA

Issue that this PR addresses

Closes #105

Checklist

PR Structure

• It is not possible to break this PR down into smaller PRs.
• This PR does not mix refactoring changes with feature changes.
• This PR's title starts with name of package that is most changed in the PR, or all if the changes are broad or impact many packages.

Thoroughness

• This PR adds tests for the new functionality or fixes.
• All updated queries have been tested (refer to this check if the data set returned by the updated query is expected to be same as the original one).

Release

• This is not a breaking change.
• This is ready to be tested in development.
• The new functionality is gated with a feature flag if this is not ready for production.

[gouthamp-stellar]

looks good overall, just one question about potentially adding a unit test