feat: add preamble to blog page

[GauravKumar17]

Description of Change

Added a warning preamble to the blog post which are more than a year old.
This helps the reader to know that some information on the blog may be outdated.

Main changes are in :

src/theme/BlogPostItem/index.tsx
src/css/custom.scss

Note- Please feel free to review and correct my mistakes, this was my life's first PR.

Checklist

• This PR was not created with AI. (PRs created mainly with AI will be closed. They waste our team's time. We ban repeat offenders.)

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Closes #857

[erickzhao]

Please remove the changes to .sha, package-lock.json, and yarn.lock

[GauravKumar17]

hey @erickzhao , This was my first PR and I mistakenly included changes to to .sha, yarn.lock, and package-lock.json thinking they were necessary, It happened due to running 'npm install' command instead of 'yarn'.
I have now removed the unintended changes . Let me know if anything else needs to be updated.
Thanks!

[dsanders11]

@GauravKumar17, can you explain why there are so many new files added in this PR?

[GauravKumar17]

@dsanders11 Thanks for reviewing !
If you are talking about the file which are along with the src/theme/BlogPostItem/index.tsx and src/css/custom.scss files , then these files were automatically generated inside the theme/BlogPostItem folder when i ran the Docusaurus-swizzle-command(Docusaurus-swizzle was mentioned in README.md file in theme folder ) to override the blogPost component to add preamble to the blog.

I understand it might look a large addition but after hours of here and there , I came to this solution.
I am happy to apply the logic differently if this solution is too heavy for this change.
Thanks

[GauravKumar17]

Hey @dsanders11 , don't mind asking but is their any mistake in the PR? If you just give me a review, I will be happy with the learning.