Fix prompts showing before required flag errors

[screspod]

What this PR does / why we need it:

Currently, when users run the install command with missing required flags (like --license), they may be prompted for optional values (like creating an admin console password if one was not provided through the --admin-console-password flag) before seeing validation errors. This creates a frustrating experience where users complete prompts unnecessarily.

This PR moves thepreRunInstall call from cobra's PreRunE to RunE to get the following order of execution and give precedence to required flag errors

Current Behavior
PreRunE
preRunInstall (prompts happen here)
Cobra's flag validation
RunE

New Behavior
PreRunE (removed, preRunInstall was the only thing in it)
Cobra's flag validation
RunE
preRunInstall (prompts happen here)

Which issue(s) this PR fixes:

https://app.shortcut.com/replicated/story/124248/cli-install-command-shows-prompts-before-required-flag-validation-errors

Does this PR require a test?

NONE

Does this PR require a release note?

NONE

Does this PR require documentation?

NONE

[github-actions]

This PR has been released (on staging) and is available for download with a embedded-cluster-smoke-test-staging-app license ID.

Online Installer:

curl "https://staging.replicated.app/embedded/embedded-cluster-smoke-test-staging-app/ci/appver-dev-3c3a1d2" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Airgap Installer (may take a few minutes before the airgap bundle is built):

curl "https://staging.replicated.app/embedded/embedded-cluster-smoke-test-staging-app/ci-airgap/appver-dev-3c3a1d2?airgap=true" -H "Authorization: $EC_SMOKE_TEST_LICENSE_ID" -o embedded-cluster-smoke-test-staging-app-ci.tgz

Happy debugging!