Support ruby 3.0.2

[semyon-estrin]

Desired Outcome

Conjur-api-ruby is running on ruby-3.0.2.

Implemented Changes

Changed default ruby version to 3.0.2.

Changed necessary code segments to adjust for ruby-3.0.2:

• Default parameters behavior in ruby 3.0.2 changed comparing to 2.X.X, when default value is nil.
• URI.escape is deprecated starting ruby-2.7, replaced with Addressable::URI.escape

Connected Issue/Story

CyberArk internal issue link: insert issue ID

Definition of Done

Tests are green with ruby-3.0.2.

Changelog

• 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
• The changes in this PR do not require tests

Documentation

• Docs (e.g. READMEs) were updated in this PR
• A follow-up issue to update official docs has been filed here: insert issue ID
• This PR does not require updating any documentation

Behavior

• This PR changes product behavior and has been reviewed by a PO, or
• These changes are part of a larger initiative that will be reviewed later, or
• No behavior was changed with this PR

Security

• Security architect has reviewed the changes in this PR,
• These changes are part of a larger initiative with a separate security review, or
• There are no security aspects to these changes

[sashaCher]

Some comments
Pay attention on backward compatibility issues

[sashaCher]

LGTM

[codeclimate]

Code Climate has analyzed commit ce2dd19 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 83.9% (0.0% change).

View more on Code Climate.