chore: prepare for GA

[dreamorosi]

Description of your changes

This PR prepares the repo for GA release(happening soon), and it introduces changes in two areas:

• Removes the pre-release warning notice from the README files and docs
• Removes the pre-release-related flags from the lerna commands in the release GH action

How to verify this change

Check the diff, check the readme files

Related issues, RFCs

N/A

PR status

Is this ready for review?: YES
Is it a breaking change?: NO

Checklist

• My changes meet the tenets criteria
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• The code coverage hasn't decreased
• New and existing unit tests pass locally and in Github Actions
• The PR title follows the conventional commit semantics

Breaking change checklist

N/A

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[github-actions]

📊 Package size report   -1.36%↓

File	Before	After
aws-lambda-powertools-commons-0.12.0-rc.1.tgz	6.5 kB	-3.66%↓6.3 kB
aws-lambda-powertools-logger-0.12.0-rc.1.tgz	24.1 kB	-1.03%↓23.8 kB
aws-lambda-powertools-metrics-0.12.0-rc.1.tgz	17.5 kB	-1.44%↓17.3 kB
aws-lambda-powertools-tracer-0.12.0-rc.1.tgz	21.4 kB	-1.13%↓21.2 kB
commons-bundle.zip	7.1 kB	-3.37%↓6.9 kB
logger-bundle.zip	24.6 kB	-0.8%↓24.4 kB
metrics-bundle.zip	18.1 kB	-1.37%↓17.8 kB
tracer-bundle.zip	22.0 kB	-1.15%↓21.7 kB
Total (Includes all files)	141.4 kB	-1.36%↓139.4 kB
Tarball size	140.2 kB	-1.29%↓138.4 kB

_{🤖 This report was automatically generated by pkg-size-action}
(options hash: 088ac866cd3815f7c5164f9a176794df)