Support OktaAuthModule.forRoot()

[denysoblohin-okta]

PR Checklist

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• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Adding Tests
• Build related changes
• CI related changes
• Documentation changes
• Other... Please describe:

What is the current behavior?

Currently the only way to import OktaAuthModule is as follows:

import { OktaAuthModule, OKTA_CONFIG } from '@okta/okta-angular';

@NgModule({
  imports: [
    ...
    OktaAuthModule
  ],
  providers: [
    { 
      provide: OKTA_CONFIG, 
      useValue: { oktaAuth } 
    }
  ],
})
export class MyAppModule { }

Issue Number: OKTA-567263

What is the new behavior?

Using forRoot() pattern to create OktaAuthModule as a singleton is a preferred way:

import { OktaAuthModule } from '@okta/okta-angular';

@NgModule({
  imports: [
    ...
    OktaAuthModule.forRoot({ oktaAuth })
  ]
})
export class MyAppModule { }

Does this PR introduce a breaking change?

• Yes
• No

Other information

Need to release this change with minor version bump (6.2.0).
Added note to MIGRATING.md about new preferred way to import OktaAuthModule as a singleton.

Reviewers