chore: add strings to en.json for smart transactions

[infiniteflower]

Description

This PR adds a number of strings to en.json for Smart Transactions, which will come out in a separate PR. I've split the much larger PR into smaller pieces to improve reviewer experience and readability.

Related issues

The much larger PR these changes have been picked from: #9315

Fixes: n/a

Manual testing steps

n/a

Screenshots/Recordings

Before

n/a

After

n/a

Pre-merge author checklist

• I’ve followed MetaMask Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud