feat: Allow additional reset password params, introduce ForgotPasswordValidator

[imorland]

Related to #3670

Allows for 3rd party extensions to extend the functionality of the Forgot Password modal. ie Adding a captcha, etc.

Changes proposed in this pull request:
ForgotPasswordModal:

• Extracts fields to an extendable function
• Extract params into an extendable function so that additional params can be added
  ForgotPasswordController
• Replaces the validator factory with a new ForgotPasswordValidator, with the same rule as existed previously
• This can be extended by 3rd party extensions to add any additional rules, where required.

Reviewers should focus on:

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)
• Related core extension PRs: (Remove if irrelevant)

[luceos]

More extensibility 💪