Feat: Add RSK Support

[zachdaniel]

Motivation

• Some application changes are required to support RSK.

Changelog

Enhancements

• Add an RSK variant, to support the configuration changes necessary, and also not call the methods that RSK doesn't support.
• A few small changes throughout, to account for slight differences in RSK responses.

• 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

I added tests to cover the incrementing of the rate limit, but I think testing the actual rate limit + wait combo itself would just introduce flaky tests at the expense of testing pretty straightforward code. I can rearchitect it to be better for that kind of testing, but that would probably take more time than it is worth.

[coveralls]

Pull Request Test Coverage Report for Build 282dfcf3-8667-40c3-85d7-1acb0ebc30c1

• 25 of 34 (73.53%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.2%) to 83.075%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/ethereum_jsonrpc/lib/ethereum_jsonrpc.ex	2	4	50.0%
apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/application.ex	6	8	75.0%
apps/ethereum_jsonrpc/lib/ethereum_jsonrpc/request_coordinator.ex	17	22	77.27%

Totals
Change from base Build cb096331-e245-4f18-ae21-d76596e543dc:	-0.2%
Covered Lines:	4403
Relevant Lines:	5300

---

💛 - Coveralls

[goodsoft]

Some questions before I approve: