make the team instance creation page look more like a page

[cstns]

Description

Made the instance form more embed-able friendly by adding the ability to hide it's title & heading.

Also removed center alignment of instance page and added a page header

Related Issue(s)

closes #3929

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 (2f654bf) to head (c65d363).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3930   +/-   ##
=======================================
  Coverage   79.28%   79.28%           
=======================================
  Files         281      281           
  Lines       12755    12755           
  Branches     2844     2844           
=======================================
  Hits        10113    10113           
  Misses       2642     2642           

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

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[cstns]

Did not add e2e tests as only cosmetic changes were made without impacting functionality