feat: update mirror node explorer configuration and add API proxy

[Neurone]

Description:

• The explorer configuration mechanism has been updated to allow the use of the latest versions.
• The mirror node API proxy was introduced to use a single endpoint for all the services (rest, rest-java, web3 and grpc). It uses the same configuration that can be found in the Mirror Node's Docker Compose file, but externalised to a separate file to align with the other configurations.

Related issue(s):

Fixes #1087

Notes for reviewer:

During the development I fixed some minor issues here and there (documentation, linter, etc.)

Checklist

• [x] Documented (Code comments, README, etc.)
• [x] Tested (unit, integration, etc.)

[lfdt-bot]

:tada: Snyk checks have passed. No issues have been found so far.

:white_check_mark: security/snyk check is complete. No issues have been found. (View Details)

:white_check_mark: license/snyk check is complete. No issues have been found. (View Details)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

@@           Coverage Diff           @@
##             main    #1125   +/-   ##
=======================================
  Coverage        ?   60.11%           
=======================================
  Files           ?       29           
  Lines           ?     1246           
  Branches        ?      157           
=======================================
  Hits            ?      749           
  Misses          ?      471           
  Partials        ?       26           

Files with missing lines	Coverage Δ
src/constants.ts	100.00% <100.00%> (ø)

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