add provider delegators

[cfaur09]

Proposed Changes

• Created a new query in elastic search service to be able to return for a given provider address all delegators ( address, stake) / delegators count
• Created a new method getProviderDelegators in ProviderService to be able to retrieve all informations from elastic
• Created a new controller providers/:contractAddress/accounts that contains also query pagination filter
• Added new unit tests for getProviderDelegators method

How to test

• providers/erd1qqqqqqqqqqqqqqqpqqqqqqqqqqqqqqqqqqqqqqqqqqqqqc0llllsayxegu/accounts -> return a list of 25 delegators
• providers/erd1qqqqqqqqqqqqqqqpqqqqqqqqqqqqqqqqqqqqqqqqqqqqqc0llllsayxegu/accounts?size=1 -> return a list of 1 delegator
• providers/erd1eztdqz4cvs23w65a50d2h2g7xer5kyjy9w33pmkrrwy0usn46u6qcryt7g/accounts -> should return [ ]
• providers/erd1qqqqqqqqqqqqqqqpqqqqqqqqqqqqqqqqqqqqqqqqqqqqqc0llllsayxegu/accounts/count -> return total delegators count

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 47.82609% with 24 lines in your changes are missing coverage. Please review.

Project coverage is 46.19%. Comparing base (0816c43) to head (22be554).

:exclamation: Current head 22be554 differs from pull request most recent head 3fe44e0. Consider uploading reports for the commit 3fe44e0 to get more accurate results

Files	Patch %	Lines
src/endpoints/providers/provider.controller.ts	33.33%	6 Missing and 2 partials :warning:
src/common/indexer/entities/provider.delegators.ts	0.00%	6 Missing :warning:
.../common/indexer/elastic/elastic.indexer.service.ts	0.00%	4 Missing :warning:
src/common/indexer/indexer.service.ts	50.00%	2 Missing :warning:
...ommon/indexer/postgres/postgres.indexer.service.ts	0.00%	2 Missing :warning:
src/endpoints/providers/provider.service.ts	80.00%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #1246 +/- ## =============================================== - Coverage 46.19% 46.19% -0.01% =============================================== Files 594 596 +2 Lines 15892 15935 +43 Branches 1707 1710 +3 =============================================== + Hits 7342 7361 +19 - Misses 6908 6929 +21 - Partials 1642 1645 +3 ``` | [Flag](https://app.codecov.io/gh/multiversx/mx-api-service/pull/1246/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=multiversx) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/multiversx/mx-api-service/pull/1246/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=multiversx) | `46.19% <47.82%> (-0.01%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=multiversx#carryforward-flags-in-the-pull-request-comment) to find out more.

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