Update V3 Zowe Explorer README GIFs and remove keytar notice

[adam-wolfe]

Proposed changes

Replace old gifs in the Zowe Explorer README.md with new ones from Zowe Docs and remove the keytar notice, since it has been over a year since keytar was replaced.

Remove unused gifs.

Release Notes

Milestone:

Changelog: n/a

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] Enhancement (non-breaking change which adds or improves functionality)
• [ ] Breaking change (a change that would cause existing functionality to not work as expected)
• [x] Documentation (Markdown, README updates)
• [ ] Other (please specify above in "Proposed changes" section)

Checklist

General

• [ ] I have read the CONTRIBUTOR GUIDANCE wiki
• [ ] All PR dependencies have been merged and published (if applicable)
• [ ] A GIF or screenshot is included in the PR for visual changes
• [ ] The pre-publish command has been executed:
  • v2 and below: yarn workspace vscode-extension-for-zowe vscode:prepublish
  • v3: pnpm --filter vscode-extension-for-zowe vscode:prepublish

Code coverage

• [ ] There is coverage for the code that I have added
• [ ] I have added new test cases and they are passing
• [ ] I have manually tested the changes

Deployment

• [ ] I have added developer documentation (if applicable)
• [ ] Documentation should be added to Zowe Docs
  • If you're an outside contributor, please post in the #zowe-doc Slack channel to coordinate documentation.
  • Otherwise, please check with the rest of the squad about any needed documentation before merging.
• [ ] These changes may need ported to the appropriate branches (list here):

Further comments

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud