Enable NPS (oppia#5383)

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## Explanation
Toggles the NPS Survey Feature Flag on.

## Essential Checklist
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- [ ] The PR title and explanation each start with "Fix #bugnum: " (If
this PR fixes part of an issue, prefix the title with "Fix part of
#bugnum: ...".)
- [x] Any changes to
[scripts/assets](https://github.com/oppia/oppia-android/tree/develop/scripts/assets)
files have their rationale included in the PR explanation.
- [x] The PR follows the [style
guide](https://github.com/oppia/oppia-android/wiki/Coding-style-guide).
- [x] The PR does not contain any unnecessary code changes from Android
Studio
([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#undo-unnecessary-changes)).
- [x] The PR is made from a branch that's **not** called "develop" and
is up-to-date with "develop".
- [x] The PR is **assigned** to the appropriate reviewers
([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#clarification-regarding-assignees-and-reviewers-section)).

## For UI-specific PRs only
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changes. -->
If your PR includes UI-related changes, then:
- Add screenshots for portrait/landscape for both a tablet & phone of
the before & after UI changes
- For the screenshots above, include both English and pseudo-localized
(RTL) screenshots (see [RTL
guide](https://github.com/oppia/oppia-android/wiki/RTL-Guidelines))
- Add a video showing the full UX flow with a screen reader enabled (see
[accessibility
guide](https://github.com/oppia/oppia-android/wiki/Accessibility-A11y-Guide))
- For PRs introducing new UI elements or color changes, both light and
dark mode screenshots must be included
- Add a screenshot demonstrating that you ran affected Espresso tests
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utility/src/main/java/org/oppia/android/util/platformparameter/FeatureFlagConstants.kt

@@ -165,7 +165,7 @@ annotation class EnableNpsSurvey
 const val ENABLE_NPS_SURVEY = "enable_nps_survey"
 
 /** Default value of the feature flag corresponding to [EnableNpsSurvey]. */
-const val ENABLE_NPS_SURVEY_DEFAULT_VALUE = false
+const val ENABLE_NPS_SURVEY_DEFAULT_VALUE = true
 
 /** Qualifier for the feature flag that toggles the new onboarding flow. */
 @Qualifier