Fix(aws-connector): Limit signing to signed headers from original request

[doodlesbykumbi]

What does this PR do?

Prior to this change the AWS connector was signing requests using all the headers present on the original request. This was resulting signature mismatches and failed auth, particularly visible when creating a new s3 bucket. With this change the aws connector will sign only the headers on the original request, it achieves this by temporarily hiding the rest of the headers before signing, then them after signing.

What ticket does this PR close?

Resolves #1430

Checklists

Change log

• [x] The CHANGELOG has been updated, or
• [ ] This PR does not include user-facing changes and doesn't require a CHANGELOG update

Test coverage

• [ ] This PR includes new unit and integration tests to go with the code changes, or
• [x] The changes in this PR do not require tests

Documentation

• [x] This PR does not require updating any documentation, or
• [ ] Docs (e.g. READMEs) were updated in this PR, and/or there is a follow-on issue to update docs

(For releases only) Manual tests

• [ ] Manually run Kubernetes-Conjur demo with a local Secretless Broker image build of your branch

[codeclimate[bot]]

Code Climate has analyzed commit 0bd30029 and detected 1 issue on this pull request.

Here's the issue category breakdown:

Category	Count
Style	1

The test coverage on the diff in this pull request is 93.7% (50% is the threshold).

This pull request will bring the total coverage in the repository to 54.8% (1.1% change).

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