Add ability to override kanister-tools image in repo controller

[pavannd1]

Change Overview

• Add helpers to get kanister-tools image if set from env
• Add ability to set env in helm chart
• Use the utility added above
• Fix repo controller tests
• Modify existing functions to use the new utility

Pull request type

Please check the type of change your PR introduces:

• 🚧 Work in Progress
• 🌈 Refactoring (no functional changes, no api changes)
• 🐹 Trivial/Minor
• 🐛 Bugfix
• 🌻 Feature
• 🗺️ Documentation
• 🤖 Test

Issues

• fixes [BUG] Repository Server tests use released version of kanister-tools image #2259

Test Plan

• 💪 Manual
• ⚡ Unit test

=== RUN   Test
START: repositoryserver_controller_test.go:71: RepoServerControllerSuite.SetUpSuite
PASS: repositoryserver_controller_test.go:71: RepoServerControllerSuite.SetUpSuite	8.814s

START: repositoryserver_controller_test.go:317: RepoServerControllerSuite.TestInvalidRepositoryPassword
PASS: repositoryserver_controller_test.go:317: RepoServerControllerSuite.TestInvalidRepositoryPassword	43.223s

START: repositoryserver_controller_test.go:521: RepoServerControllerSuite.TearDownSuite
PASS: repositoryserver_controller_test.go:521: RepoServerControllerSuite.TearDownSuite	0.061s

OK: 1 passed
--- PASS: Test (52.10s)
PASS
ok  	github.com/kanisterio/kanister/pkg/controllers/repositoryserver	54.022s

• 💚 E2E

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[PrasadG193]

LGTM