Alter application instance creation page to resemble a standalone page

[cstns]

Description

• General styling made to the Application instance creation page.
• Extracted common application instance non-representational functionality into separate mixin which will also allow to move entire state in the vuex store later on.
• added an additional slot to the SectionNavigationHeader which allows replacing the existing breadcrumbs, required because of the custom format of the breadcrumbs of the create instance page

Related Issue(s)

closes #3933

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.28%. Comparing base (7163e5d) to head (3df957a).

Additional details and impacted files

@@                                                Coverage Diff                                                @@
##           3934-refresh-the-page-while-creating-an-aplication-does-not-load-teams-correctly    #3947   +/-   ##
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  Files                                                                                   281      281           
  Lines                                                                                 12755    12755           
  Branches                                                                               2844     2844           
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  Hits                                                                                  10113    10113           
  Misses                                                                                 2642     2642           

Flag	Coverage Δ
backend	79.28% <ø> (ø)

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