Add inputs 'update-toolchains-only', 'update-env-javahome', 'add-to-env-path'

Changes in detail:
------------------
- action.yml:
  - add inputs:
    - update-toolchains-only
    - update-env-javahome
    - add-to-env-path
  - update description for input "overwrite-settings"
  - remove default value of input "overwrite-settings",
    since the default is now propagated from input 'update-toolchains-only'

- base-models.ts:
  - extend interface JavaInstallerOptions:
    - add fields:
      - updateEnvJavaHome: boolean;
      - addToEnvPath: boolean;

- constants.ts:
  - add constant INPUT_UPDATE_TOOLCHAINS_ONLY
    = 'update-toolchains-only'

- auth.ts:
  - function configureAuthentication():
    - add parameter:
      - overwriteSettings: boolean
    - remove the now obsolete const overwriteSettings

- toolchains.ts:
  - function configureToolchains(...):
    - add parameter updateToolchains: boolean
    - remove the now obsolete const overwriteSettings
  - improve variable naming:
    - rename any occurrence of 'overwriteSettings'
        by 'updateToolchains'
    - add field updateToolchains: boolean to the parameter object
  - function writeToolchainsFileToDisk(...):
    - improve variable naming:
      - rename variable 'settingsExists'
          by 'toolchainsExists'
    - update wording of info logs to be more applicable

- setup-java.ts:
  - interface installerInputsOptions:
    - rename to IInstallerInputsOption to meet common coding convention
    - add fields:
      - updateToolchainsOnly: boolean;
      - overwriteSettings: boolean;
      - updateEnvJavaHome: boolean;
      - addToEnvPath: boolean;
  - function run():
    - add const:
      - const updateToolchainsOnly:
        - get as boolean from input 'update-toolchains-only', default: false
      - const overwriteSettings:
        - get as boolean from input 'overwrite-settings', default: !updateToolchainsOnly
      - const updateEnvJavaHome:
        - get as boolean input 'update-env-javahome', default: !updateToolchainsOnly
      - const addToEnvPath:
        - get as boolean input 'add-to-env-path', default: !updateToolchainsOnly
   - extend const installerInputsOptions to match with IInstallerInputsOption:
      - add field updateToolchainsOnly
      - add field overwriteSettings
      - add field updateEnvJavaHome
      - add field addToEnvPath
    - update call of auth.configureAuthentication()
        to auth.configureAuthentication(overwriteSettings)
  - function installVersion(...):
    - add const and init from parameter options:
      - updateToolchainsOnly, overwriteSettings,
        updateEnvJavaHome, addToEnvPath
    - init the additional fields of installerInputsOptions accordingly
    - call toolchains.configureToolchains(...):
      - with parameter updateToolchains= overwriteSettings || updateToolchainsOnly

- base-installer.ts:
  - add constants to import from constants:
    - INPUT_UPDATE_JAVA_HOME
    - INPUT_ADD_TO_PATH
  - add fields:
    - protected updateEnvJavaHome: boolean;
    - protected addToEnvPath: boolean;
  - ctor:
    - init these fields from JavaInstallerOptions accoprdingly
  - function setJavaDefault(...):
    - if updateEnvJavaHome is false:
      - SKIP updating env.JAVA_HOME
      - log info:
        `Skip updating env.JAVA_HOME according to ${INPUT_UPDATE_JAVA_HOME}`
    - if addToEnvPath is false:
      - SKIP adding toolchain path to env.PATH
      - log info:
        `Skip adding to env.PATH according to ${INPUT_ADD_TO_PATH}`

action.yml

@@ -43,9 +43,21 @@ inputs:
     description: 'Path to where the settings.xml file will be written. Default is ~/.m2.'
     required: false
   overwrite-settings:
-    description: 'Overwrite the settings.xml file if it exists. Default is "true".'
+    description: 'Overwrite the settings.xml file if it exists. Default is "!update-toolchains-only". If explcitly set "true", it will update settings.xml regardless of "update-toolchains-only"'
     required: false
-    default: true
+    # DO NOT set a default here! The default will be propagated from input 'update-toolchains-only'!
+  update-toolchains-only:
+    description: 'Update toolchains.xml only. Default is "false". No update of settings.xml, no update of JAVA_HOME, no adding to PATH by default - unless "overwrite-settings", "update-env-javahome" or "add-to-env-path" are not explicitly set "true"'
+    required: false
+    default: false
+  update-env-javahome:
+    description: 'Update the JAVA_HOME environment variable. Default is "!update-toolchains-only"'
+    required: false
+    # DO NOT set a default here! The default will be propagated from input 'update-toolchains-only'!
+  add-to-env-path:
+    description: 'Add "<JDK home>/bin" to the PATH environment variable. Default is "!update-toolchains-only"'
+    required: false
+    # DO NOT set a default here! The default will be propagated from input 'update-toolchains-only'!
   gpg-private-key:
     description: 'GPG private key to import. Default is empty string.'
     required: false