Add setup for GitHub pages

[kolchfa-aws]

Description

Sets up the necessary config and styling files for the GitHub pages theme.

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[dbwiddis]

Am I the only one who thinks the OpenSearch logo looks like a tilted smiley? (ツ)

[dbwiddis]

The build.gradle failure on javadoc/spotless are fixed by #827, please merge or rebase.

[dbwiddis]

LGTM, holding off on merging until opensearch-project/OpenSearch#8588 is merged, so that backport works more smoothly.

[kolchfa-aws]

Sure, but I don't think we need to backport this one though. It should work off the main branch only.

[owaiskazi19]

Sure, but I don't think we need to backport this one though. It should work off the main branch only.

@kolchfa-aws we will be releasing SDK in 2.9 from 1.x branch. I think the branch should be updated with the latest document changes. @dbwiddis IMO we should backport this to 1.x.

[dbwiddis]

@dbwiddis IMO we should backport this to 1.x.

These docs live on a single branch (I'm not sure exactly which repo, but a gh-pages branch usually.) They won't get published from another branch. Probably doesn't hurt to backport but will never be read under current config.