HOSTEDCP-1156: Add defaulting webhook to installation and notes

[bryan-cox]

What this PR does / why we need it:
Adds the enable-defaulting-webhook flag to the hypershift install and a note about the flag only being available for OCP versions greater than or equal to 4.14.

Adds note to create cluster command that either the release-image or release-stream flag is needed when the enable-defaulting-webhook is not available.

Which issue(s) this PR fixes:
Fixes HOSTEDCP-1156

Checklist

• Subject and description added to both, commit and PR.
• Relevant issues have been referenced.
• This change includes docs.
• This change includes unit tests.

[openshift-ci-robot]

@bryan-cox: This pull request references HOSTEDCP-1156 which is a valid jira issue.

In response to this:

What this PR does / why we need it:
Adds the enable-defaulting-webhook flag to the hypershift install and a note about the flag only being available for OCP versions greater than or equal to 4.14.

Adds note to create cluster command that either the release-image or release-stream flag is needed when the enable-defaulting-webhook is not available.

Which issue(s) this PR fixes:
Fixes HOSTEDCP-1156

Checklist

• Subject and description added to both, commit and PR.
• Relevant issues have been referenced.
• This change includes docs.
• This change includes unit tests.

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[openshift-ci]

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[bryan-cox]

Adds documentation requested in #2892 (comment)

[muraee]

/lgtm

[jparrill]

/lgtm

[enxebre]

/approve
/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bryan-cox, enxebre

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[openshift-ci]

@bryan-cox: all tests passed!

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