Closes #18: feature: Add WebSecurity to EUM Server

[ClaudioWaldvogel]

Closes #18

This change is 

[heiko-holz]

Reviewed 19 of 19 files at r1, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @ClaudioWaldvogel)

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src/main/java/rocks/inspectit/oce/eum/server/configuration/model/security/authProvider/SimpleApiTokenAuthenticationProviderSettings.java line 43 at r1 (raw file):

    private String defaultFileName;

    private boolean createDefaultFileIfNotExists = true;

why do we need the boolean?
Wouldn't it be sufficient to check if defaultFileName is not empty?

As far as I can see, defaultFileName is only used in SimpleApiAuthenticationProvider#createDefaultTokenProviderFile.

What happens if defaultFileName is set but createDefaultFileIfNotExists=false?

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src/main/java/rocks/inspectit/oce/eum/server/utils/DirectoryPoller.java line 68 at r1 (raw file):

     * Flag to indicate that we need to shutdown the used executor on destroy.
     */
    private boolean isDefaultExecutor = false;

Shouldn't it rather say
Flag to indicate that the {@link #defaultExecutor()} is executed, which needs to be shut down on destroy?

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src/main/java/rocks/inspectit/oce/eum/server/utils/DirectoryPoller.java line 97 at r1 (raw file):

    public DirectoryPoller start() {
        pollingTask = executor.scheduleWithFixedDelay(this::pollChanges, frequencyInMillis, frequencyInMillis, TimeUnit.MILLISECONDS);

should we start with an initial delay of frequencyInMillis or start immediately?

[MariusBrill]

Reviewed 7 of 19 files at r1, 2 of 6 files at r2, 1 of 6 files at r3, 6 of 6 files at r4, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @ClaudioWaldvogel)

[MariusBrill]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @ClaudioWaldvogel)

[MariusBrill]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @ClaudioWaldvogel)

[heiko-holz]

Reviewed 2 of 2 files at r5, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ClaudioWaldvogel)