Allow also whitespace ` ` (together with `T`) as a separator between
date and time parts of the timestamp string. E.g.:
```
{ts '2020-02-08 12.10.45'}
```
or
```
{ts '2020-02-08T12.10.45'}
```
Fixes: #46069
(cherry picked from commit 07c977023fb8ceab5991c359a6cbfe07beaad9bb)
27265f032a