Align the unreachable devfile exception message

[vinokurig]

What does this PR do?

Add a common exception message and use it for cases when:

• The devfile location is unavailable.
• The devfile content is is not valid: e.g the response content is an html content of an scm authorisation page.

Screenshot/screencast of this PR

What issues does this PR fix or reference?

fixes eclipse-che/che#22469

How to test this PR?

1. Deploy che from the PR image: quay.io/eclipse/che-server:pr-615
2. Start a workspace from a private GitHub repo, see the error:
   
3. Start a workspace from a private azure-devops repo, see the error in the same format:
   

PR Checklist

As the author of this Pull Request I made sure that:

• The Eclipse Contributor Agreement is valid
• Code produced is complete
• Code builds without errors
• Tests are covering the bugfix
• The repository devfile is up to date and works
• Sections What issues does this PR fix or reference and How to test this PR completed
• Relevant user documentation updated
• Relevant contributing documentation updated
• CI/CD changes implemented, documented and communicated

Reviewers

Reviewers, please comment how you tested the PR when approving it.

[vinokurig]

/retest

[vinokurig]

/retest

[artaleks9]

/retest

[vinokurig]

/retest

[artaleks9]

• Verified on Che without any PAT/OAuth setup with quay.io/eclipse/che-server:pr-615 for a factory of private repository Azure-DevOps/Bitbucket.org/GitLab.com/github.com/ git providers. The exception message is the same format.
• @vinokurig
  One thing: need to uncomment the line in the test-azure-no-pat-oauth-flow.sh (and delete the comment):
  https://github.com/eclipse-che/che-server/blob/main/.ci/openshift-ci/test-azure-no-pat-oauth-flow.sh#L30

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: artaleks9, tolusha, vinokurig

The full list of commands accepted by this bot can be found here.

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• OWNERS

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[artaleks9]

/retest

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server : 3.x :: Build 57245083 : quay.io/devspaces/server-rhel8:3.11-18
SUCCESS; copied to quay; /DS_CI/push-latest-container-to-quay_3.x/3795 triggered

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