text update needed on Dashboard Settings

[LaurenWags]

Description

Per the spec for SNTP, Show Background Image should be updated to Show Background Images.

Steps to Reproduce

1. Clean profile
2. Enable SNTP from flags, relaunch
3. Open Dashboard Settings on NTP

Actual result:

Expected result:

Should say Show Background Images

Reproduces how often:

easily

Brave version (brave://version info)

Brave	1.5.62 Chromium: 79.0.3945.130 (Official Build) nightly (64-bit)
Revision	e22de67c28798d98833a7137c0e22876237fc40a-refs/branch-heads/3945@{#1047}
OS	macOS Version 10.14.6 (Build 18G103)

Version/Channel Information:

• Can you reproduce this issue with the current release?
• Can you reproduce this issue with the beta channel?
• Can you reproduce this issue with the dev channel?
• Can you reproduce this issue with the nightly channel? yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information:

cc @brave/legacy_qa @rebron @petemill

[gupta437]

If no one is working actively on this issue, Can I take this issue to work on?

[bsclifton]

@gupta437 it's all yours! 😄 Let me know if you need help finding where it's stored