Allow signup page to be customised from admin settings

[knolleary]

Description

In 1.3 we added branding.account.signUpTopBanner to flowforge.yml as a way to insert custom text above the sign-up form.

Via #1621 we have a requirement to insert longer text next to the sign-up form.

The downside of using flowforge.yml is that is requires a platform restart to pickup changes - making it hard to iterate.

This PR allows the Admin to set the content for both pieces of HTML via the Admin Settings screen - if 'allow signup' is enabled.

If will still use the value of branding.account.signUpTopBanner from flowforge.yml unless overridden via this new setting. The only limitation being you cannot set it to blank via admin settings and have that override a value from the yml file (blank is interpreted as unset, so the yml file value gets used). The right answer being to remove it from flowforge.yml as a one-off admin task.

The new setting branding:account:signUpLeftBanner does not, as of the current state of this PR, get displayed anywhere. That is over to @joepavitt to add.

Related Issue(s)

#1621

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 flowforge/helm to update ConfigMap Template
  • Issue/PR raised on flowforge/CloudProject to update values for Staging/Production

Labels

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

[joepavitt]

real working demo:

[joepavitt]

Demo (fyi @iskerrett)

Screen.Recording.2023-02-10.at.13.27.46.mov

[joepavitt]

adding @Pezmc as reviewer given that I've since contributed directly to this PR

[joepavitt]

expecting E2E tests to fail, just pushing progress to-date so that someone can sub in to finish if required ahead of Thursday as I'm blocked out in meetings for 1.5 days between now and then

[joepavitt]

Verified in Staging #1621 (comment)