chore(docs): improve READMEs for individual providers

[xiehan]

Couple of minor but IMO powerful improvements to the provider READMEs:

• Puts the true underlying version number in the title instead of the tracked version (I have never ever found the tracked version to be helpful in practice)
• Includes a link to the Registry page earlier on in the document (I look for this often and hate having to scroll so far down to find it)
• Removes text about "This links to the minimum version being tracked" which is no longer relevant as a result of Mark's changes merged in feat: added underlying terraform provider version to readme #342

It's worth noting that in the snapshot tests, underlyingTerraformVersion is always unset, but in the actual provider repos in practice, it is always set. See here for an example: https://github.com/cdktf/cdktf-provider-aws/blob/main/README.md

[github-actions]

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