UserId module: define getEid method & SharedId Id submodule: support for recently added eid object fields

[patmmccann]

We need to allow the publisher to define inserter via config for the sharedid module

See https://github.com/InteractiveAdvertisingBureau/openrtb2.x/blob/main/2.6.md#objecteid

We should incorporate the comment below to allow id submodules to define a getEid method into the requirements and label the pr as having that feature

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Attribute | Type | Description
-- | -- | --
inserter | string | The canonical domain name of the entity (publisher, publisher monetization company, SSP, Exchange, Header Wrapper, etc.) that caused the ID array element to be added. This may be the operational domain of the system, if that is different from the parent corporate domain, to facilitate WHOIS and reverse IP lookups to establish clear ownership of the delegate system.This should be the same value as used to identify sellers in an ads.txt file if one exists.For ad tech intermediaries, this would be the domain as used in ads.txt. For publishers, this would match the domain in the site or app object.
source | string | Canonical domain of the ID.
matcher | string | Technology providing the match method as defined in mm.In some cases, this may be the same value as inserter.When blank, it is assumed that the matcher is equal to the sourceMay be omitted when mm=0, 1, or 2.
mm | int | Match method used by the matcher. Refer to List: ID Match Methods in AdCOM 1.0

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</html>Attribute        	Type                    	Description
inserter	string	The canonical domain name of the entity (publisher, publisher monetization company, SSP, Exchange, Header Wrapper, etc.) that caused the ID array element to be added. This may be the operational domain of the system, if that is different from the parent corporate domain, to facilitate WHOIS and reverse IP lookups to establish clear ownership of the delegate system.

This should be the same value as used to identify sellers in an ads.txt file if one exists.

For ad tech intermediaries, this would be the domain as used in ads.txt. For publishers, this would match the domain in the site or app object.
source	string	Canonical domain of the ID.
matcher	string	Technology providing the match method as defined in mm.

In some cases, this may be the same value as inserter.

When blank, it is assumed that the matcher is equal to the source

May be omitted when mm=0, 1, or 2.
mm	int	Match method used by the matcher. Refer to [List: ID Match Methods](https://github.com/InteractiveAdvertisingBureau/AdCOM/blob/main/AdCOM%20v1.0%20FINAL.md#list-id-match-methods-) in AdCOM 1.0

[dgirardi]

Given an ID module's EID defition def, and an ID value id, the EID is currently defined as:

{
   source: def.getSource?.(id) ?? def.source,
   uid: [{
       id: def.getValue?.(id) ?? id,
       atype: def.atype,
       ext: def.getUidExt?.(id)
   }],
   ext: def.getEidExt?.(id)
}

Proposal

Instead of the above, ID modules can provide a function taking the ID value (such as def(id)) and returning the full EID.