[docs] Update manual installation steps for installing Expo modules in bare React Native (#21797)

[docs] Update installing Expo modules guide

[android] Fix building error from outside of project root (#15109)

# Why

our gradle script will break if building from outside of the project root. especially for appcenter to build a monorepo pr

[android] Fix building error from outside of project root (#15109)

# Why

our gradle script will break if building from outside of the project root. especially for appcenter to build a monorepo project, the gradle execution is in this case: `./packages/sdk43mono/android/gradlew -p packages/sdk43mono/android :app:assembleDebug`

fixes #14944

# How

passing working directory for [`String.execute`](https://docs.groovy-lang.org/latest/html/groovy-jdk/java/lang/String.html#execute(java.lang.String[],%20java.io.File))

# Test Plan

1. monorepo test repo: https://gitlab.com/kudochien/rnmono and run with `./packages/sdk43mono/android/gradlew -p packages/sdk43mono/android :app:assembleDebug`. note that this repo is include the fixes.
2. test from bare-expo:

```sh
cd $HOME
/path/to/expo/apps/bare-expo/android/gradlew -p /path/to/expo/apps/bare-expo/android :app:assembleDebug
```

Co-authored-by: Tomasz Sapeta <[email protected]>

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[docs] Add installing-expo-modules doc and hide/update unimodules guide (#14807)