[docs] Move third-party integrations to root level of left-hand nav, add more catalogs

[rmoff]

This PR moves third-party integrations up to the root level of the docs, to make the docs intuitive for users and developers alike.
It incorporates #13612 which adds additional third-party catalogs

Unexpanded view (changes shown in red)

Expanded view (changes/moves highlighted)

---

Redirects added for 3rd party integration pages so that links (e.g. /docs/nightly/amoro/) still work (now /integrations/amoro/)

Links updated (and a fair few existing broken anchors fixed) and verified using muffet—outstanding errors are for existing broken links (which I'll log a separate issue for):

$ brew install muffet
$ muffet -b 8196 -c 32 --exclude maven.org --exclude getdaft --exclude=javadoc/1 --exclude linkedin --exclude amazon.com --exclude dremio --exclude cloudera --exclude github --exclude maven.apache.org --exclude mvnrepository.com --exclude starrocks.io --exclude doris.apache.org --exclude docs/1 --exclude docs/latest http://localhost:8000/
http://localhost:8000/integrations/dell/
        403     https://www.dell.com/en-us/dt/storage/ecs/index.htm
http://localhost:8000/how-to-release/
        id #stagingRepositories not found       https://repository.apache.org/#stagingRepositories
http://localhost:8000/docs/nightly/kafka-connect/
        id #view/Microsoft_AAD_IAM/TenantProperties.ReactView not found https://portal.azure.com/#view/Microsoft_AAD_IAM/TenantProperties.ReactView
        id #view/Microsoft_AAD_RegisteredApps/ApplicationsListBlade not found   https://portal.azure.com/#view/Microsoft_AAD_RegisteredApps/ApplicationsListBlade
http://localhost:8000/status/
        403     https://crates.io/crates/iceberg
http://localhost:8000/docs/nightly/hive/
        404     https://spark.apache.org/docs/2.4.3/sql-data-sources-parquet.html#configuration
http://localhost:8000/spark-quickstart/
        error when dialing [::1]:8888: dial tcp [::1]:8888: connect: connection refused http://localhost:8888
http://localhost:8000/integrations/risingwave/
        id #catalog not found   https://docs.risingwave.com/integrations/destinations/apache-iceberg#catalog
http://localhost:8000/vendors/
        id #use-a-catalog-integration not found https://docs.snowflake.com/en/user-guide/tables-iceberg#use-a-catalog-integration
        id #use-snowflake-as-the-iceberg-catalog not found      https://docs.snowflake.com/en/user-guide/tables-iceberg#use-snowflake-as-the-iceberg-catalog

[nastra]

@rmoff can you please elaborate why files are being moved around? For example, view-configuration.md is moved from docs/docs/view-configuration.md to site/docs/concepts/view-configuration.md. We keep stuff under docsthat are version-specific and other things under site that apply across all Iceberg versions, so moving those files isn't something that we would want to do

[rmoff]

@rmoff can you please elaborate why files are being moved around? For example, view-configuration.md is moved from docs/docs/view-configuration.md to site/docs/concepts/view-configuration.md. We keep stuff under docsthat are version-specific and other things under site that apply across all Iceberg versions, so moving those files isn't something that we would want to do

Fair question. #13618 Added a Java heading to the docs, so the intention here is to split out docs that are related to Iceberg and not Java-specific.

[rmoff]

@nastra @manuzhang please take another look at this. I've reverted the changes that move Concepts, so they remain where they are.
This PR now just moves the 3rd party integrations out from under "Java" and to a root level in the nav, making it easier for Iceberg users to find them.

[manuzhang]

@rmoff Can you update PR title and PR description accordingly? It'll be great to have a latest snapshot of the website after this change.

[rmoff]

@manuzhang thanks - title and description updated, new snapshot images added. WDYT?

[kevinjqliu]

LGTM! slight nit

[kevinjqliu]

nit: my preference would be for this PR to solely be refactor. and have another follow up PR to change the content, i.e. adding new catalogs