Add RESET_VALUE configuration value as sentinel value to reset a config option.

[taeold]

Instead of allowing nulls to reset a configuration value, we are introducing a new sentinel value, RESET_VALUE to make it clear the intention of resetting the config value to platform default:

import * as functions from "firebase-functions/v1";
import { onRequest } from "firebase-functions/v2/https";
import { RESET_VALUE } from "firebase-functions/v2/options";

export const v1Req = functions
  .runWith({
    minInstances: functions.RESET_VALUE,
    memory: functions.RESET_VALUE,
    serviceAccount: RESET_VALUE
  }).https.onRequest(
    (req, res) => {
      res.sendStatus(200)
    },
);

export const v2Req = onRequest(
  {
   memory: RESET_VALUE,
   minInstances: RESET_VALUE,
  },
  (req, res) => {
    res.sendStatus(200)
  },
);

Majority of this PR concerns fixing/updating typings on various configuration options.

Recall that in v2, we inlined/repeat all function options in each respective providers to make reference doc more clear. This unfortunately bloated up this PR since I had to repeat the changes in each and every provider.

[taeold]

Current dependencies on/for this PR:

• master
  • PR Functions SDK v4 #1161
    • PR Add RESET_VALUE configuration value as sentinel value to reset a config option. #1250 👈
    • PR Add new option to preserveExternalChanges. #1253
      • PR Fix broken test. #1254

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[TheIronDev]

Had a few questions to make sure some changes were intentional, otherwise LGTM