Return gasPrice at gettxinfo API's method

[saneery]

#2348

Motivation

Add gasPrice field at the result of gettinfo method

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so if necessary

[coveralls]

Pull Request Test Coverage Report for Build 0a74354c-01f8-4786-bbe8-51d7c5cba9e2

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 80.933%

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Totals
Change from base Build e8dae500-635c-4255-b6c3-0243d5e67b8e:	0.003%
Covered Lines:	5204
Relevant Lines:	6430

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💛 - Coveralls

[ayrat555]

Please add json schema test so we won't lose anything in the future

[saneery]

Please add json schema test so we won't lose anything in the future

@ayrat555 what the schema? where can I find an example?

[ayrat555]

@saneery https://en.wikipedia.org/wiki/JSON#JSON_Schema

we didn't test JSON schema yet but I think it's time to start. this PR is a good opportunity https://github.com/jonasschmidt/ex_json_schema

[ayrat555]

@saneery are you going to resolve my comment? I didn't get an answer in 2 weeks

[saneery]

@ayrat555 maybe it should be different PR since we need to add a new dependency?
Maybe we should create a new issue to add JSON schema tests?