Update version to 2.15

[EvgenyUglov]

Description

Update all 2.14 references to 2.15.

GitHub Issues

List the GitHub issues impacted by this PR:

GitHub Issue #
https://github.com/dell/csm/issues/1896

Checklist:

• I have performed a self-review of my own code to ensure there are no formatting, vetting, linting, or security issues
• I have verified that new and existing unit tests pass locally with my changes
• I have not allowed coverage numbers to degenerate
• I have maintained at least 90% code coverage
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have executed the openshift end-to-end test scenarios without enabling any modules
• Backward compatibility is not broken

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

• Built image
• Ran unit tests

[github-actions]

Merging this branch will not change overall coverage

Impacted Packages	Coverage Δ	🤖
github.com/dell/csi-powerstore/core/semver	0.00% (ø)

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Coverage by file

Changed unit test files

• github.com/dell/csi-powerstore/core/semver/semver_test.go