executor, config: update the way to show array config items when using show config (#16712)

[sre-bot]

cherry-pick #16712 to release-4.0

---

What problem does this PR solve?

Issue Number: close #16704

After #16229, we can use show config to get configs of PD and TiKV.
If some config item is an array, it will be flattened and each element of it is shown in an individual row, which is not user-friendly.
For example, the config item engines = ["tikv", "tiflash", "tidb"] will be shown as:

+------+--------------+--------------------------+---------+
| Type | Instance     | Name                     | Value   |
+------+--------------+--------------------------+---------+
| tidb | 0.0.0.0:4000 | isolation-read.engines.0 | tikv    |
| tidb | 0.0.0.0:4000 | isolation-read.engines.1 | tiflash |
| tidb | 0.0.0.0:4000 | isolation-read.engines.2 | tidb    |
+------+--------------+--------------------------+---------+

After this PR, it will be shown as:

+------+--------------+--------------------------+------------------------------+
| Type | Instance     | Name                     | Value                        |
+------+--------------+--------------------------+------------------------------+
| tidb | 0.0.0.0:4000 | isolation-read.engines   | ["tikv", "tiflash", "tidb"]  |
+------+--------------+--------------------------+------------------------------+

This new format is easier to understand and safer to update.

Check List

Tests

• Unit test

[sre-bot]

/run-all-tests

[qw4990]

Wait for #16082.

[qw4990]

wait for #16475.

[qw4990]

/run-all-tests

[wshwsh12]

LGTM

[qw4990]

/run-sqllogic-test-2

[zz-jason]

LGTM