datalist: add all and match_by attributes to filter blocks

[tdyas]

Several improvements to the datalist library used by some of the data sources in this provider:

• Adds an all attribute to filter blocks. When set to true (i.e., all = true), a filter block will only match if all of the values match the given field. This is useful when matching against multi-valued fields (e.g., lists and sets).

• Adds a match_by attribute to filter blocks to allow string-matching to use regular expressions and substring matches. Set match_by = "re" for regular expression matching and match_by = "substring" for substring matching. This makes add digitalocean_domains data source #484 actually useful because domains can then be matched by regular expressions.

• Also refactors the filter support so that values are parsed once and not when filter blocks are applied.

Caveats:

• The docs still need updating.

• Is substring matching redundant with regular expression matching? I kept it in because it could be faster but maybe not worth it given regular expression matching can accomplish the same result.

[andrewsomething]

👍 Great stuff! This is really useful.

Is substring matching redundant with regular expression matching? I kept it in because it could be faster but maybe not worth it given regular expression matching can accomplish the same result.

As it's already there, I think it's worth keeping it around. Some people find regex intimidating and for simple uses-cases it's less to think about.

[tdyas]

Okay, I made the suggested edits again.