Enable key placeholder to be combined with other data within the same command argument

[filipecosta90]

Fixes #153
This PR adds the option to combine key placeholders with other characters within the same argument. This is important for RedisGraph and RediSearch for us to be able to mix for example node ids with other conditions, etc...
I've used this feature on RG 2.0 benchmark and forgot to open the PR to kick off this feature discussion.
Example of usage:

memtier_benchmark -c 10 -t 1 \
    --command="graph.query GRAPH1 \"MATCH (s:vertex)-[*6]->(t) WHERE id_in_graph(s)=__key__ RETURN count(t)\"" \
    --key-maximum=100000 --distinct-client-seed --command-key-pattern G --key-prefix=""

This PR includes two extra tests

[kaplanben]

Checkmarx One – Scan Summary & Details – 17e560b2-a5ed-4416-ac23-6f96b3b9fb9a

New Issues (8)

Checkmarx found the following issues in this Pull Request

Severity	Issue	Source File / Package	Checkmarx Insight
	Divide_By_Zero	/run_stats_types.cpp: 230	details The application performs an illegal operation in aggregate_average, in /run_stats_types.cpp. In line 230, the program attempts to divide by st... ID: EEHnUgVgJ%2FwgXcxq7WHuFdT3ksE%3D Attack Vector
	Divide_By_Zero	/run_stats_types.cpp: 231	details The application performs an illegal operation in aggregate_average, in /run_stats_types.cpp. In line 231, the program attempts to divide by st... ID: oj6Z8K7CiAgqAWkz86DiNhTfGK0%3D Attack Vector
	Divide_By_Zero	/run_stats_types.cpp: 254	details The application performs an illegal operation in summarize, in /run_stats_types.cpp. In line 254, the program attempts to divide by test_durat... ID: cmgK30ZZRdLy7AdfDjHTSHXUeY8%3D Attack Vector
	Divide_By_Zero	/run_stats_types.cpp: 253	details The application performs an illegal operation in summarize, in /run_stats_types.cpp. In line 253, the program attempts to divide by test_durat... ID: hCRjVteC9p7VT8WfdcnHumVvl4Q%3D Attack Vector
	Divide_By_Zero	/deps/hdr_histogram/hdr_histogram.c: 1186	details The application performs an illegal operation in hdr_percentiles_print, in /deps/hdr_histogram/hdr_histogram.c. In line 1186, the program att... ID: w%2FT7Et7mcbBjyoLvnFURUWT5%2FPg%3D Attack Vector
	Divide_By_Zero	/deps/hdr_histogram/hdr_histogram.c: 1169	details The application performs an illegal operation in hdr_percentiles_print, in /deps/hdr_histogram/hdr_histogram.c. In line 1169, the program att... ID: z2R%2BCcGvs8KjP8j2W79nCyO7O9c%3D Attack Vector
	Divide_By_Zero	/deps/hdr_histogram/hdr_histogram.c: 1184	details The application performs an illegal operation in hdr_percentiles_print, in /deps/hdr_histogram/hdr_histogram.c. In line 1184, the program att... ID: Xed9lnTk6uwhYNuXEGx52%2F0bkl8%3D Attack Vector
	Divide_By_Zero	/deps/hdr_histogram/hdr_histogram.c: 1185	details The application performs an illegal operation in hdr_percentiles_print, in /deps/hdr_histogram/hdr_histogram.c. In line 1185, the program att... ID: hUrw8ZO0MwgenXfN8SO91RVNuoM%3D Attack Vector

Fixed Issues (9)

Great job! The following issues were fixed in this Pull Request

Severity	Issue	Source File / Package
	Buffer_Improper_Index_Access	/cluster_client.cpp: 335
	Buffer_Improper_Index_Access	/cluster_client.cpp: 327
	Divide_By_Zero	/deps/hdr_histogram/hdr_histogram.c: 1172
	Divide_By_Zero	/memtier_benchmark.cpp: 1330
	Divide_By_Zero	/memtier_benchmark.cpp: 1329
	Divide_By_Zero	/memtier_benchmark.cpp: 1329
	Divide_By_Zero	/memtier_benchmark.cpp: 1330
	Divide_By_Zero	/memtier_benchmark.cpp: 1327
	Divide_By_Zero	/obj_gen.cpp: 444