feat: implement web support for Firebase Remote Config

[Salakar]

Description

Remote config web rework as part of: #6979

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[google-cla]

All (the pull request submitter and all commit authors) CLAs are signed, but one or more commits were authored or co-authored by someone other than the pull request submitter.

We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that by leaving a comment that contains only @googlebot I consent. in this pull request.

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[russellwheatley]

@googlebot I consent.

[pr-Mais]

LGTM

[lesnitsky]

LGTM