ATLAS-5384: Atlas Classic UI: Upgrade UI dependencies for dashboardv2

[Brijesh619]

What changes were proposed in this pull request?

The legacy dashboardv2 module requires dependency upgrades to address outdated sub-packages and close open Dependabot pull requests. Because dashboardv2 is tied to the older npm v6 build environment via Maven, attempting to upgrade deeply nested sub-dependencies using manual resolutions or overrides is unsupported.

This PR cleanly resolves the outdated dependencies and vulnerabilities by natively upgrading their top-level parent build tools in package.json to exact pinned versions.

Changes include:

1. Upgraded grunt to 1.6.3 (Inherently pulls in a modernized version of micromatch to resolve picomatch vulnerabilities - PR Bump picomatch from 2.3.1 to 2.3.2 in /dashboardv2/public/js/external_lib/atlas-lineage #588 & PR Bump picomatch from 2.3.1 to 2.3.2 in /dashboardv2 #579).
2. Upgraded grunt-contrib-connect to 5.0.1 (Inherently pulls in modernized versions of serve-static and send vulnerabilities - PR Bump serve-static from 1.14.1 to 1.16.2 in /dashboardv2 #254 & PR Bump send and serve-static in /dashboardv2 #253).
3. Upgraded grunt-contrib-cssmin to 4.0.0 (Inherently resolves nested clean-css and trim-newlines vulnerabilities while retaining strict Node 12 compatibility).
4. Removed ineffective overrides blocks from package.json to rely entirely on native, safe npm dependency resolution.
5. Regenerated a clean package-lock.json (lockfileVersion: 1) using the strictly enforced Node v12.16.0 / npm v6.13.7 environment.

How was this patch tested?

• Manual Node/NPM Test: Cleared node_modules and ran npm install inside dashboardv2 using the project-mandated Node v12.16.0 and npm v6.13.7 binaries to guarantee lockfile compatibility.
• Audit Verification: Ran npm audit to confirm that the picomatch, serve-static, send, clean-css, and trim-newlines vulnerabilities are completely eliminated from the dependency tree.
• Maven Build Test: Verified the full build passes successfully by running mvn clean -DskipTests -Drat.skip=false package -Pdist,embedded-hbase-solr from the root directory.

[Brijesh619]