add script to help override flag value locally

Add a script to help to create flag value building rules.

The script will only extract necessary information from the value file
but it will not validate the file. The validation will defer to building
system.

For input

```
flag_value {
    package: "com.android.aconfig.test"
    name: "disabled_ro"
    state: DISABLED
    permission: READ_ONLY
}
flag_value {
    package: "com.android.demoapp.test"
    name: "enabled_ro"
    state: DISABLED
    permission: READ_WRITE
}
flag_value {
    package: "com.android.aconfig.test"
    name: "enabled_rw"
    state: ENABLED
    permission: READ_WRITE
}
```

The output Android.bp file will be like
```
VALUE_LIST_LIST = [
    aconfig-local-com.android.demoapp.test,
    aconfig-local-com.android.aconfig.test
]

aconfig_values {
    name: "aconfig-local-com.android.demoapp.test",
    package: "com.android.demoapp.test",
    srcs: [
        "override_values.textproto",
    ]
}

aconfig_values {
    name: "aconfig-local-com.android.aconfig.test",
    package: "com.android.aconfig.test",
    srcs: [
        "override_values.textproto",
    ]
}
```

Bug: 298692416
Test: source build/envsetup.sh && overrideflags, and then check the
output

Change-Id: Ife4063e079811e0b29046be7a6bc127cad668ed0

tools/overrideflags.sh

@@ -0,0 +1,99 @@
+#!/bin/bash -e
+# Copyright (C) 2023 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+source $(cd $(dirname $BASH_SOURCE) &> /dev/null && pwd)/../../make/shell_utils.sh
+require_top
+
+function print_help() {
+    echo -e "overrideflags is used to set default value for local build."
+    echo -e "\nOptions:"
+    echo -e "\t--release-config  \tPath to release configuration directory. Required"
+    echo -e "\t--no-edit         \tIf present, skip editing flag value file."
+    echo -e "\t-h/--help         \tShow this help."
+}
+
+function main() {
+    while (($# > 0)); do
+        case $1 in
+        --release-config)
+            if [[ $# -le 1 ]]; then
+                echo "--release-config requires a path"
+                return 1
+            fi
+            local release_config_dir="$2"
+            shift 2
+            ;;
+        --no-edit)
+            local no_edit="true"
+            shift 1
+            ;;
+        -h|--help)
+            print_help
+            return
+            ;;
+        *)
+            echo "$1 is unrecognized"
+            print_help
+            return 1
+            ;;
+        esac
+    done
+
+
+
+    case $(uname -s) in
+        Darwin)
+            local host_arch=darwin-x86
+            ;;
+        Linux)
+            local host_arch=linux-x86
+            ;;
+        *)
+            >&2 echo Unknown host $(uname -s)
+            return
+            ;;
+    esac
+
+    if [[ -z "${release_config_dir}" ]]; then
+        echo "Please provide release configuration path by --release-config"
+        exit 1
+    elif [ ! -d "${release_config_dir}" ]; then
+        echo "${release_config_dir} is an invalid directory"
+        exit 1
+    fi
+    local T="$(gettop)"
+    local aconfig_dir="${T}"/build/make/tools/aconfig/
+    local overrideflag_py="${aconfig_dir}"/overrideflags/overrideflags.py
+    local overridefile="${release_config_dir}/aconfig/override_values.textproto"
+
+    # Edit override file
+    if [[ -z "${no_edit}" ]]; then
+        editor="${EDITOR:-$(which vim)}"
+
+        eval "${editor} ${overridefile}"
+        if [ $? -ne 0 ]; then
+            echo "Fail to set override values"
+            return 1
+        fi
+    fi
+
+    ${T}/prebuilts/build-tools/${host_arch}/bin/py3-cmd -u "${overrideflag_py}" \
+        --overrides "${overridefile}" \
+        --out "${release_config_dir}/aconfig"
+}
+
+
+main "$@"