doc: add a brief rfc about TiDB sequence (#16682)
doc: add a brief rfc about TiDB sequence (#16682)


ngaut/tidb,XuHuaiyu/tidb,coocood/tidb,c4pt0r/tidb,kyle-wang/tidb,kyle-wang/tidb,kyle-wang/tidb,EvilMcJerkface/tidb,kyle-wang/tidb,ngaut/tidb,ngaut/tidb,ngaut/tidb,coocood/tidb,kyle-wang/tidb,EvilMcJerkface/tidb,c4pt0r/tidb,c4pt0r/tidb,kyle-wang/tidb,pingcap/tidb,c4pt0r/tidb,pingcap/tidb,pingcap/tidb,pingcap/tidb,pingcap/tidb,c4pt0r/tidb,ngaut/tidb,XuHuaiyu/tidb,ngaut/tidb,pingcap/tidb,c4pt0r/tidb