Add regex to import filters (see Explora)

[PhilReedData]

Is your feature request related to a problem? Please describe

• More flexible options when adding to the allow and block list filters when importing. Use regular expression option with free text.

Describe the solution you'd like

• See Explora (Canada) who have already done this. (Their scenario: avoid multiple providers sharing the same events and being duplicated).

Additional context

• Risk of very complex regex taking up much CPU cycles, so limit somehow (eg string length)
• Raised at focus group 2026-01-27