Add BigQuery relation naming macros for concurrent execution

[RRap0so]

Implements BigQuery-specific relation naming macros to enable concurrent dbt execution without relation name collisions, matching functionality available in PostgreSQL adapter.

resolves #1359

Problem

The BigQuery adapter lacks standardized relation naming macros that are available in other adapters like PostgreSQL. This creates several issues:

1. Concurrent execution conflicts: When multiple dbt instances run simultaneously (CI/CD pipelines, parallel development environments), temporary relations can have naming conflicts since there's
   no collision prevention mechanism
2. Adapter inconsistency: PostgreSQL adapter provides make_temp_relation, make_intermediate_relation, make_backup_relation, and make_relation_with_suffix macros, but BigQuery does not, creating
   inconsistent experiences across adapters
3. Limited materialization patterns: Complex materializations that require standardized temporary, intermediate, and backup relation naming cannot rely on consistent macro interfaces

Before this PR, BigQuery users had no standardized way to generate unique temporary relation names during concurrent dbt executions, leading to potential relation conflicts and failed runs.

Solution

Implemented four BigQuery-specific relation naming macros in adapters.sql that mirror the PostgreSQL adapter's functionality:

• bigquery__make_relation_with_suffix: Core macro that handles identifier truncation to respect BigQuery's 1024 character limit and optional datetime stamping
• bigquery__make_temp_relation: Creates temporary relations with unique datetime suffixes for collision prevention
• bigquery__make_intermediate_relation: Creates intermediate relations without datetime suffixes
• bigquery__make_backup_relation: Creates backup relations with configurable types (e.g., table → view)

Bonus

PostgreSql adapter wasn't tested, this commit adds tests for both to ensure nothing breaks.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

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