feat: Query service client

[asmyasnikov]

• extract session pool into indipendent package (internal/session_pool ?) #981
• switch table client to new session pool #982
• design query service client interface #983
• implement query service client #984
• embed new session pool into query service client #985
• Implement indexed scanner #1074
• Implement named scanner #1075
• Implement struct scanner #1076
• SLO test over query service #1084
• Basic example with query-service client #1089
• traces over internal/query.Client internals #1100
• traces over internal/pool.Pool internals #1101
• logs over internal/query.Client #1102
• opentelemetry over internal/query.Client #1103
• metrics over internal/query.Client #1104
• database/sql driver over query-service (enabled by opt-in) #1201
• table option for redirect table.Session.Execute queries to query.Execute #1197
• table option for redirect table.Session.StreamExecuteScanQuery queries to query.Execute #1198
• table option for redirect table.Session.ExecuteSchemeQuery queries to query.Execute #1199
• driver initialize option for redirect all table queries to query.Execute #1200

[flymedllva]

Is query.Client a replacement for table.Client? Or will the API move from query.Client to table.Client?