[A11y] Add label for ProfileListActivity

Task

Introduce label for ProfileListActivity as Profile List.

Reference PR: https://github.com/oppia/oppia-android/pull/2750

When you create a PR for this, make sure you add test to check the functionality. Also, suggest working on this PR only if its your first or second PR to Oppia-Android project.

General Explanation

When Talkback is on, whenever we click on any option which leads to new screen the reader will automatically read the label associated with that screen first. If in case label in not present then it will read app name i.e. Oppia.

Example

https://user-images.githubusercontent.com/9396084/108906068-78b75080-7646-11eb-943e-212e29fc3e98.mp4

In this above video as soon as we double-tap Battery, new screen is opened. The reader first outputs Battery followed by Navigate up, Button and finally Battery again. In this the first Battery output is the label of this new screen which indicates the learner which screen is opened. The second Battery is because we selected the title in the screen and it’s just reading that text. So we need labels for various screens general which matches the title but if the title is dynamic then we need static label.

[rt4914]

Can I work on this issue? @prayutsu I might need some help in testing as I am fairly new to contributing.

@Karanjot-singh This issue is already assigned to @AnubhavPabby

[prayutsu]

@arjunrkaushik As @AnubhavPabby claimed it first, we should assign this issue to him, but I am assigning you #2819 which is almost similar to this. Can you please add a comment there so can I assign that issue to you?