branch-3.0: [Improve](Variant) pick random backend as coordinator #45754

[github-actions]

Cherry-picked from #45754

[hello-stephen]

Thank you for your contribution to Apache Doris.
Don't know what should be done next? See How to process your PR.

Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[hello-stephen]

run buildall

[doris-robot]

TPC-H: Total hot run time: 40428 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpch-tools
Tpch sf100 test result on commit 6395d88bd4050b76e48925c20967ea9d1848c160, data reload: false

------ Round 1 ----------------------------------
q1	17664	7390	7205	7205
q2	2058	168	156	156
q3	10733	1073	1136	1073
q4	10549	710	713	710
q5	7735	2834	2810	2810
q6	233	145	142	142
q7	951	597	592	592
q8	9348	1941	1988	1941
q9	6559	6398	6461	6398
q10	6966	2323	2287	2287
q11	470	256	261	256
q12	410	215	208	208
q13	17787	2964	2989	2964
q14	254	213	206	206
q15	580	526	528	526
q16	675	618	609	609
q17	974	602	591	591
q18	7255	6537	6677	6537
q19	1392	1072	976	976
q20	473	221	193	193
q21	3892	3081	3144	3081
q22	1074	967	978	967
Total cold run time: 108032 ms
Total hot run time: 40428 ms

----- Round 2, with runtime_filter_mode=off -----
q1	7274	7177	7455	7177
q2	324	231	229	229
q3	2869	2869	2877	2869
q4	1982	1776	1847	1776
q5	5705	5701	5694	5694
q6	225	141	139	139
q7	2185	1760	1779	1760
q8	3336	3531	3517	3517
q9	8751	8889	8820	8820
q10	3529	3515	3518	3515
q11	610	490	505	490
q12	806	605	588	588
q13	16473	3119	3146	3119
q14	328	271	289	271
q15	552	509	511	509
q16	723	677	673	673
q17	1850	1622	1606	1606
q18	8307	7682	7642	7642
q19	7481	1628	1482	1482
q20	2069	1829	1893	1829
q21	5495	5240	5289	5240
q22	1122	1008	1025	1008
Total cold run time: 81996 ms
Total hot run time: 59953 ms

[doris-robot]

TPC-DS: Total hot run time: 195888 ms

machine: 'aliyun_ecs.c7a.8xlarge_32C64G'
scripts: https://github.com/apache/doris/tree/master/tools/tpcds-tools
TPC-DS sf100 test result on commit 6395d88bd4050b76e48925c20967ea9d1848c160, data reload: false

query1	1285	918	895	895
query2	6254	2040	2030	2030
query3	10970	4271	4166	4166
query4	66813	27344	23453	23453
query5	5478	445	455	445
query6	526	173	178	173
query7	6151	309	315	309
query8	331	247	214	214
query9	9211	2668	2665	2665
query10	516	258	251	251
query11	17949	14997	15906	14997
query12	159	100	97	97
query13	1581	417	416	416
query14	10869	7439	7320	7320
query15	219	175	176	175
query16	7227	562	491	491
query17	1109	567	583	567
query18	1884	335	333	333
query19	209	153	157	153
query20	114	110	107	107
query21	68	44	41	41
query22	4787	4680	4563	4563
query23	34688	34043	34193	34043
query24	5774	2922	2805	2805
query25	513	413	403	403
query26	683	163	163	163
query27	1886	291	297	291
query28	4469	2525	2543	2525
query29	684	437	430	430
query30	254	168	162	162
query31	1012	814	844	814
query32	65	52	51	51
query33	432	285	269	269
query34	922	484	509	484
query35	857	732	739	732
query36	1069	937	952	937
query37	124	66	73	66
query38	4033	3923	3971	3923
query39	1542	1458	1453	1453
query40	140	86	84	84
query41	49	51	51	51
query42	118	100	101	100
query43	528	499	499	499
query44	1149	792	793	792
query45	188	175	175	175
query46	1152	754	744	744
query47	2030	1900	1917	1900
query48	465	370	378	370
query49	734	394	394	394
query50	844	412	423	412
query51	7409	7181	7147	7147
query52	101	94	86	86
query53	259	192	183	183
query54	568	456	445	445
query55	78	79	82	79
query56	265	254	237	237
query57	1178	1094	1120	1094
query58	213	203	214	203
query59	3155	2918	2976	2918
query60	299	256	250	250
query61	128	128	128	128
query62	779	654	671	654
query63	209	190	203	190
query64	1850	665	613	613
query65	3219	3185	3140	3140
query66	660	308	288	288
query67	15799	15308	15352	15308
query68	4575	545	548	545
query69	456	249	249	249
query70	1162	1067	1129	1067
query71	426	244	248	244
query72	6667	3927	3892	3892
query73	761	336	343	336
query74	10072	9035	8877	8877
query75	3316	2655	2600	2600
query76	2565	1109	1130	1109
query77	482	268	263	263
query78	10740	9668	9553	9553
query79	7722	571	577	571
query80	2031	421	421	421
query81	573	247	237	237
query82	1081	143	117	117
query83	244	150	143	143
query84	281	77	78	77
query85	1476	287	282	282
query86	485	269	270	269
query87	4545	4201	4219	4201
query88	5372	2348	2333	2333
query89	406	282	288	282
query90	2227	184	178	178
query91	181	146	144	144
query92	68	48	50	48
query93	6500	533	526	526
query94	906	289	292	289
query95	343	244	243	243
query96	629	272	274	272
query97	3339	3134	3212	3134
query98	214	198	208	198
query99	1618	1292	1298	1292
Total cold run time: 337746 ms
Total hot run time: 195888 ms