add bridge file docs

[Dana Bauer (danabauer)]

What's in this PR?

• bridge file page with schema and query examples
• updates to "what is GERS?" page
• update sidebar
• GERS demonstration page to draft

To do

• update the id examples with the new UUIDs as soon as we publish the June data
• move queries to separate directory and use querybuilder in the doc

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https://github.com/OvertureMaps/docs/actions/workflows/publish-pr-to-staging.yml

[Copilot]

Pull Request Overview

This PR focuses on updating the GERS documentation with a new bridge file page, refreshed information on the GERS system, and a draft demonstration page.

• Adds a comprehensive Bridge Files page with schema details and examples.
• Updates the "What is GERS?" page to clarify the framework.
• Marks the GERS Demonstrations page as a draft.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
docs/gers/index.mdx	Updated description text and system table information for clarity.
docs/gers/gers-demonstrations.mdx	Added a draft flag to indicate work in progress.
docs/gers/bridge-files.mdx	Introduced a new Bridge Files page with detailed schema, examples, and usage instructions.

Comments suppressed due to low confidence (1)

docs/gers/bridge-files.mdx:71

• [nitpick] The description for the 'between' property appears unclear. Consider revising 'the dataset way takes' to a clearer explanation, such as 'the proportion of the feature's total length captured by the dataset.'

| `between` | array | represents the portion of the normalized length of the GERS feature the dataset way takes, represented by a range between 0 and 1