refactor(core,grpc-sdk,module-tools): rework service-discover, health checking and module communication

[kkopanidis]

This PR re-works the health checking and service discovery systems of the core module, to facilitate proper load-balancing and high-availability for module connections.

Brief changes:

• Modules now get an instance id that publish to the core module
• Modules are represented as a collection of instances with separate addresses.
• Health checking is happening on individual services based on their calling IP, not their published URL
• Core publishes list of addresses or the published URL if it is a domain

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other (please describe)

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the main branch
• When resolving a specific issue, it's referenced in the PR's description (e.g. fix #xxx, where "xxx" is the issue number)

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature

Other information: