Update ADOT JS `getting-started` page and links

[jj22ee]

Issue #, if available:

Description of changes:

• Update getting-started page to be more similar to Python and Java, and add more references to ADOT.

Testing: Check changes in:

• https://github.com/jj22ee/aws-otel.github.io/blob/test-merge-approval/src/docs/getting-started/javascript-sdk.mdx
• https://github.com/jj22ee/aws-otel.github.io/blob/test-merge-approval/src/docs/getting-started/js-sdk/trace-metric-auto-instr.mdx#sample-applications

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