Update content to use sentence casing

### **Description**

Currently, we are inconsistent with our content casing conventions across the app.

This is a problem because although subtle it causes inconsistencies across our app and impacts our brand, accessibility and the message we convey to our users.

In order to solve this problem, all content should use sentence casing unless it falls into the valid exceptions. For a more comprehensive description [see the PR for the same issue in extension](https://github.com/MetaMask/metamask-extension/pull/15285)

### Exceptions to sentence case
#### Names, companies, abbreviations or nouns
e.g. “MetaMask”, “OpenSea”, “Google Chrome”, “Ledger Live”, “NFT”, “API”

#### Special terms
e.g. “Secret Recovery Phrase”, "Private Key"
"Secret Recovery Phrase' and "Private Key" an extremely important concepts that are critical to preventing users losing their funds. To convey the importance of these terms, they use title case.

#### Page navigation
When referring to the navigation route in the app we quote the page as its title appears e.g.

"You can enable Ledger Live support by clicking Settings > Advanced > Use Ledger Live.”
"Go to Settings > Advanced”
“Go to Settings > Network and enter the chain ID. You can find the chain IDs of most popular networks on $1”

### **Technical Details**

- Update all content in `locales/languages/en.json` that should use sentence case to use sentence case

### **Acceptance Criteria**

- All content that should use sentence case should be sentence cased

### **References**

- [Extension PR for the same issue](https://github.com/MetaMask/metamask-extension/pull/15285)