[Fix](connector) encode doris http url path segments for non-ascll identifiers

[liujiwen-up]

Proposed changes

Issue Number: close #xxx

Problem Summary:

This PR fixes failures when Doris database/table identifiers contain non-ASCII characters, such as Chinese table names.

Previously, the connector built several Doris HTTP API URLs by directly concatenating database/table names into the path, for example:

• /api/{db}/{table}/_schema
• /api/{db}/{table}/_query_plan
• /api/{db}/{table}/_stream_load
• /api/{db}/_stream_load_2pc
• /api/enable_light_schema_change/{db}/{table}
• /api/query/default_cluster/{db}

When the table name contains Chinese characters, Flink SQL planning may fail while fetching schema or query plan from Doris FE.

This PR adds a shared DorisUrlUtils helper to encode each HTTP path segment with UTF-8 percent encoding, and updates the related REST, Stream Load, Batch Stream Load, 2PC commit, and schema change paths to use it.

The change only encodes HTTP URL path segments. It does not change table.identifier, SQL identifier quoting, Stream Load labels, headers, or COPY mode behavior.

Added unit tests for:

• URL path segment encoding
• schema and query plan URLs
• Stream Load URLs
• Batch Stream Load URLs
• 2PC commit URLs
• schema change URLs

Checklist(Required)

1. Does it affect the original behavior: Yes
2. Has unit tests been added: Yes
3. Has document been added or modified: No Need
4. Does it need to update dependencies: No
5. Are there any changes that cannot be rolled back: No

Further comments

Validation:

mvn -Pflink1 -pl flink-doris-connector-base -Dtest=DorisUrlUtilsTest,TestRestService,TestDorisStreamLoad,TestDorisBatchStreamLoad,TestDorisCommitter,SchemaChangeManagerTest test

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